Blue Diamond

"You cannot fathom how much I've mourned — what thousands of years of grief has done to me!"

Blue Diamond is a Homeworld Gem and a member of the Great Diamond Authority that rules over the Gem race. She first appears in a flashback in "The Answer" and debuts in person in "Steven's Dream".

Appearance
As one of the rulers of Homeworld, Blue Diamond has a massive size, with her towering height making her own Pearl appear tiny in comparison. However, her somewhat hunched posture, combined with her long, sweeping cloak, gives her a relatively smaller and more despondent silhouette than if she were standing straight.

Her complexion is azure, and she has long, straight, alice blue hair which curls inward at the ends. Two noticeable and symmetrical locks of her hair curl and point inwards towards her face just below her cheekbones. She has a long ovoid face, a full upper lip, and a straight nose. She also possesses large, sad, downward-slanting eyes with bold mascara on the lower lashes, giving the appearance of a weeping woman – most likely due to her depression over the supposed shattering of Pink Diamond. Her irises are light blue with black diamond-shaped pupils and she has thin arching eyebrows.

Her gemstone is located on her chest above her sternum, and she wears a long navy blue cloak that touches the ground. Underneath the upper part of her cloak, she wears a navy blue hood. Her height is similar to Yellow Diamond, only obscured by her hunched posture making her look shorter.

Personality
Blue Diamond's debut portrays her as a very mellow Diamond who treats high-ranking members of her court with respect. According to Holly Blue Agate, Blue Diamond has a reputation for mercy and forgiveness. "Saving" Greg from the threat of the Cluster after taking a liking to him, unaware that the Cluster is no longer active, demonstrates this. Another example of Blue being merciful is when she restrained herself from attacking Rose Quartz (Steven) and gives him a chance to speak. However, as with Yellow Diamond, her true nature may be at odds with her reputation, as she sentences Ruby to be shattered for accidentally fusing with Sapphire while trying to do her job and saving her.

Blue Diamond's temperament appears to have changed significantly in the 5,000 years following the shattering of Pink Diamond. She fell into a state of depression after Pink Diamond was shattered. She is unable to let go of the past, becoming fixated on preserving Pink Diamond's legacy. Her efforts to maintain the late diamond's zoo, save Earth specimens from the Cluster's emergence, and her refusal to shatter the Rose Quartzes that once served under Pink Diamond shows this behavior. She continues to regard the Earth as Pink Diamond's colony, and, due to being unaware that the Cluster is bubbled, is visibly saddened by the fact that the planet will eventually be destroyed.

Additionally, Blue Diamond seems to not understand humans, given by how she was surprised that Greg was able to comprehend and sympathize with her pain of losing a loved one, though this is understandable since she is not native to earth and has had very little reason to get to know humans.

Blue Diamond, as shown in the episode "The Trial", is extremely diplomatic. Against Yellow Diamond's wishes, she allowed Steven to continue making his case during his trial, though she did lose her temper when his recounting of events differed. She nonetheless seemed to want to hear Blue Zircon's theory on how and why Pink Diamond was shattered. When Yellow Diamond snaps and poofs both Zircons present at the trial, Blue Diamond confronts her and scolds her for not having enough restraint to hear the case out. This shows that Blue Diamond may be as merciful and forgiving as her gems claim – at the very least, she certainly has a greater respect for due process and an interest in the truth.

In "Reunited", despite her unreasoning aggression towards the Crystal Gems, Steven later heard Blue's thoughts, that despite seeking to do them harm it only made the pain she felt worsen and her longing to see Pink grow.

After learning of Rose Quartz and Pink Diamond being the same person, she has shown concern over Steven along with Yellow Diamond. She has also shown extreme affection for Steven/Pink as seen through the effect her powers have on those around her, as along with extreme sentimentalism causing Yellow to have to reign her in. During the events of "Familiar", Blue is shown to have a humorous side to her, poking fun at Steven's name.

However, despite her more merciful and forgiving nature, she is shown to be extremely unforgiving and derogatory towards fusions of different gems, something that she shares in common with Yellow Diamond. This is first seen when Blue Diamond sentenced Ruby to be shattered just for fusing with Sapphire out of a desire to save her life, demonstrating her ruthlessness towards these situations. Even after 5,000 years, her attitude towards these situations has not changed. When conversing with Steven, she mocked Garnet's fusion and stated that she didn't belong anywhere. Then, when Steven and Connie fused, Blue Diamond lashed out at Steven, viewing such a fusion as extremely inappropriate, and demanded they unfuse immediately. She also had no qualms about locking Steven up as punishment for his actions.

Ancient History
Not much is known about Blue Diamond's exact past. Over the course of thousands of years, Blue Diamond amassed a great amount of respect, colonies, and Gems. When Pink Diamond was eventually created, Blue and the other Diamonds grew a close relationship with her. Blue found Pink's immature personality to be charming at times, but would also tend to be strict on her under specific circumstances. In "Familiar", Blue recalls a time where Pink named a batch of Pyrite "Fool's Gold" to White Diamond's dismay. She also recalls the many times her, Yellow, and White would gather at her pool area, where Pink would sing underneath the water while they would attempt to guess the song. Blue, along with the other Diamonds, would also attend the many parties Pink would hold in celebration of the Diamond Authority's achievements.

Over 6,000 Years Ago
When Pink realizes the beauty of her colony, Earth, and wishes to cease the colonization process, Blue gathered humans from their families and gave Pink the Zoo.

Over 5,750 Years Ago
Unbenknownst to Blue and the other Diamonds, Pink has created her alter-ego Rose Quartz and rebelled alongside her Pearl to form the Crystal Gems. In retalliation, Blue Diamond gathers her court and calls upon a Sapphire to Earth's Cloud Arena to know what Rose's next move would be. She later thanks Sapphire for receiving her vision that the Crystal Gems would soon attack the Cloud Arena, believing the Rebellion would end that day.

When the Crystal Gems eventually show up, Blue Diamond flees in her palanquin, but later threatens to shatter Ruby when she accidentally fuses with Sapphire during the bedlam.

On the Moon Base, Blue scolds Pink for continuously coming up with excuses to cease colonization, and reassures her that as long as she maintains positivity, her Gems would reflect that and inevitably end the Rebellion.

Around 5,000 Years Ago
When Pink stages her own shattering and continues her life as Rose Quartz, Blue is flung into a deep depression. In addition to taking over Pink's Zoo, Blue becomes obsessed with preserving anything that is related to Pink, and remains in a constant state of mourning and regret for thousands of years.

Around 4,500 Years Ago
Along with the other Diamonds, Blue assists in unleashing the Corrupting Light with the hopes of wiping out all Gems on Earth, but instead causes any Gems exposed to the light to become Corrupted.

"The Answer"
After Rose Quartz and Pearl rebelled, Blue Diamond called Sapphire to Earth to share a vision of the future. Once Sapphire explains what the rebels will do on the Cloud Arena, Blue Diamond thanks Sapphire for her vision. Once Rose and Pearl show up, Blue Diamond's Palanquin grows spider legs to get her to safety and protect her. Blue Diamond is later disgusted by Ruby and Sapphire's fusion, threatening to shatter Ruby for fusing with a member of her court.

"Steven's Dream"
Blue Diamond returns to Earth one last time to pay her respects to Pink Diamond before, as she believes, the Cluster will emerge, unaware that Steven had contained the superweapon months earlier. Blue Diamond expresses regret over how she should have done more, and wonders what Pink Diamond would think of the Cluster destroying her colony. After Greg reveals himself, Blue Diamond asks her Pearl to bring Greg to her. She then states how she is impressed by humanity's ability to survive in the wild and remarks on the irony that a fragile human can survive on Earth while a being as powerful as a Diamond can perish. When Greg tells her that he also lost someone close to him, Blue Diamond is surprised that a human can sympathize with her, and is glad that she can save Greg from the Cluster. She forcefully takes Greg and boards her ship with the goal of bringing him to Pink Diamond's Zoo.

"Gem Heist"
Holly Blue Agate reveals that after Pink Diamond was shattered, Blue Diamond took over her Zoo in an attempt to preserve her legacy. Blue Diamond and Holly Blue have been maintaining the Zoo since Era 2 began.

"That Will Be All"
Blue Diamond returns to the Zoo to mourn alongside a room full of bubbled Rose Quartzes. She is shocked to find Yellow Diamond entering the room and tells her that she just wants to cry alone. Blue Diamond listens to Yellow Diamond's song, comforts Yellow when it ends, and is greeted afterward by Holly Blue Agate and the Crystal Gems. Blue Diamond does not understand what Holly Blue means by Sapphire's "special delivery". Once Sapphire lies and tells her that she foresaw Blue Diamond requesting more humans for the zoo, Blue Diamond believes her and is sad to announce that there is limited time to retrieve more humans due to the Cluster.

"The Trial"
Blue Diamond and Yellow Diamond both act as judges for Steven's trial. Blue Diamond first appears beside Yellow Diamond after her Pearl introduces her. She wonders where Rose Quartz is, and when Yellow suggests shattering Rose just for "looking like that", Blue Diamond says she wants to hear her make her case. She also states that she wants to punish Rose for what she did to Pink Diamond. After listening to the prosecuting Zircon's case, Steven tells the Diamonds that he shattered Pink Diamond, prompting Blue Diamond to ask Steven how he did it. Steven doesn't know how so he makes up a story, but when he brings up the Breaking Point, Blue Diamond loses her composure and causes the whole room to cry. She states that Rose shattered Pink Diamond with a sword. After the court takes a short recess, the defending Zircon presents evidence that shows Rose couldn't have shattered Pink Diamond, which surprises Blue Diamond. Eventually, the defending Zircon unintentionally accuses the Diamonds of being capable of such a thing, shocking Blue Diamond. When Yellow Diamond poofs both the prosecuting and defending Zircon, Blue Diamond yells at her to stop, asking her to restrain herself. Immediately after, she is surprised when Steven and Lars hijack her palanquin and escape through the ceiling.

"Raising the Barn"
Steven tells Lapis and Peridot about his Homeworld adventure, describing his trial in front of the Diamonds and subsequent escape in a commandeered palanquin, much to Peridot and Lapis' shock. Afraid that the Diamonds will eventually find them on Earth, Lapis leaves the planet.

"Your Mother and Mine"
Blue Diamond appears in Garnet's story of Rose Quartz. Alongside Yellow and White Diamond, she helps corrupt most of the remaining Gems on Earth at the end of the Rebellion.

"Can't Go Back"
Blue Diamond appears in Steven's dream about the Diamonds. She advises Pink Diamond to deal with the growing Rebellion on Earth shortly before the latter's assassination. After Steven informs Lapis Lazuli about his dream, she misunderstands its meaning, causing her to abandon Earth and the moon forever.

"A Single Pale Rose"
Blue Diamond does not appear in this episode; however, she is mentioned twice. The first time indirectly by Gem War Pearl who says "There was a bright light and everyone was – why did I do it?" The bright light is referring to the light the remaining Diamonds used to corrupt the remaining Rebellion. The second time she is mentioned is by Rose Quartz when talking with Pearl. She says "Blue and Yellow don't care! They never have!" just before turning back to Pink Diamond to feign her shattering.

"Now We're Only Falling Apart"
Blue and Yellow Diamond appear in Pearl's flashback about Pink Diamond. Pink pleads with them to spare the Earth, but they both refuse to listen, forcing her to begin the Rebellion as Rose Quartz.

"Reunited"
Blue and Yellow Diamond arrive on Earth during Garnet's wedding to awaken the Cluster. While Yellow Diamond is busy fighting the Cluster, Blue Diamond lands on the beach and engages in combat with Steven, Connie, Pearl, Amethyst, Garnet, Bismuth, and Peridot. After a brief fight, Blue easily overpowers all of them. Garnet stands up to Blue Diamond and clings onto her leg. This is then revealed to be a distraction while Lapis Lazuli, who now joins the fray, drops the barn on Blue Diamond. Blue quickly recovers, however, and retaliates until the Cluster seemingly crushes her with her and Yellow's ships. With help from Yellow Diamond, Blue recovers and continues to fight until Steven convinces her to stand down by revealing that he is Pink Diamond, which Blue Diamond is overjoyed by.

"Legs From Here to Homeworld"
Blue Diamond appears hugging Steven and crying tears of joy and relief after finding out that Pink Diamond was not shattered. This causes the surrounding Gems to cry tears as well, which Pearl explains to Connie to be one of her powers. Blue Diamond later explains that she, along with White Diamond and Yellow Diamond, blasted the planet Earth in order to obliterate all the Gems on the surface, indicating that she was not aware of the attack causing corruption. After Steven takes the Crystal Gems, Yellow Diamond, and Blue Diamond to see Nephrite, Blue and Yellow Diamond use their abilities to partially stabilize her. Later, she accompanies Steven, the Crystal Gems, and Yellow Diamond to Homeworld aboard Pink Diamond's ship, which she becomes emotional about. She describes White Diamond as being "difficult" and seems worried about meeting with her. She is last seen when Steven is taken to White Diamond by White Pearl.

"Familiar"
Blue Diamond meets Steven in her pool, where she talks, to begin with cheerfully and saying how happy she is that Pink Diamond (as Steven) is back on homeworld, but then soon turns to lamenting on how sad it was after Pink left. Before Steven can try and talk to her about White, she leaves for an appointment of some sort.

"Together Alone"
Steven and Pearl ask Yellow and Blue to have a ball to give them an opportunity to talk to White. Blue and Yellow agree, giving them their Pearls to help. Blue later appears telling Steven to not fool around, and then asks if he is going looking like he is. She then says that Steven cannot bring his friends, but Steven says they can be inspiring, and Blue lets them come, but only if Amethyst wears limb enhancers and Garnet defuses. She then walks off, telling Steven that she’ll take care of everything. Blue arrives at the ball with her Pearl, and tells Steven that he is doing great. However when Steven and Connie fuse, she is shocked and disgusted, telling Steven that if they don’t unfuse she will make them. Blue then watches as Steven's friends leap in to protect him, but are poofed by Yellow.

Abilities
Being a Diamond, Blue Diamond is one of the most powerful Gems in the entire Gem Empire, who demonstrated the ability to take on the Crystal Gems by herself. It can be assumed that she possesses standard Gem abilities, but since she is a Diamond, the abilities are expected to be much greater than usual. Due to her large size, she is able to lift up a human, such as Greg, with relative ease. She also has extreme durability, as after the Crystal Gems literally threw themselves at her, and she was hit by Pearl, Amethyst, Garnet, Bismuth, Lion's sonic roar, and Steven's spiked bubble, she fell onto her knees, but quickly recovered, and seemingly suffered minimal damage from being crushed first under a barn and then her own warship. In "Reunited", she is noted to have astounding mental strength.

Unique Abilities

 * Aura Projection: The Diamonds can project an aura around them that they can control, they can either radiate it from their entire bodies or emit it from specific parts of their bodies, usually their hands. Blue's aura is blue and has water-like properties. Though intangible, Blue was able to break Lapis' water chains from her hands upon coating her hands with her aura. She can use this as an offensive ability in both the physical and mental plane, as seen when she was able to focus her aura and attack Steven as he was projecting.
 * Radiated Pathokinesis: Blue Diamond can engulf a large area with her aura, causing any Gem, Half-Gem and sometimes even human within it to feel an emotion of Blue's choosing. An involuntary induction of sorrow was powerful enough to cause Gems exposed to the aura to break down and cry immediately unprovoked, even affecting Yellow Diamond to a small degree. When she weaponized her grief over Pink Diamond's supposed death, she instantly rendered the Crystal Gems unable to fight, also splitting all but the most stable Gem fusions that got caught in her aura apart, as Alexandrite came undone as soon as she was affected, while Garnet remained whole. The level of resistance to the ability varies. Non-human animals are apparently impervious, as demonstrated by Lion. Humans are unaffected as seen with Connie, as she was able to move. Gems who feel that they have endured emotional trauma worse than the feelings induced by the aura can resist it almost completely, as Lapis Lazuli barely shed a tear upon being hit by the aura. This ability passively affects nearby Gems and Half-Gems whenever Blue Diamond is shedding tears in any emotional state (such as joy or nostalgia), albiet to a lesser degree since she doesn't radiate her blue aura during these instances.
 * Corruption Induction: Though the attack was meant to obliterate the Crystal Gems on Earth after Pink's supposed shattering, Blue, Yellow, and White Diamond's collective powers instead corrupted the remaining Gems on Earth.
 * Corruption Reversal: As demonstrated on Centipeetle in "Legs From Here to Homeworld", Blue Diamond, along with Yellow Diamond, Steven (as Pink Diamond), and presumably White Diamond, has the ability to reverse the effects of the Corrupting Light on Gems. However, it is implied that this is only temporary without the power of all four Diamonds.
 * Psychic Resistance: Blue Diamond's aura shields her from telepathic abilities such as Pink Diamond's even without her own awareness, briefly repelling Steven with the sheer intensity of her thoughts. She was also able to locate Steven on the mental plane when he was not in physical contact with her.
 * Psychic Blast: While on the mental plane, Blue Diamond can fire her aura as a beam which induces profound distress in the target; however, despite combining her assault with Yellow Diamond's, it was repelled by Steven's own aura.
 * Energy Projection: She is shown to have some form of energy projection power that she uses for battle. The energy can be molded into different projectiles, from spheres to a hail of lasers, or combinations thereof.
 * Energy Construction: Once Blue Diamond broke free of Lapis water chains, she was able to create a ball of stellar light and it was able to shoot out blasts and explosions.
 * Enhanced Strength: She is able to break Rose's sword with just the snap of her fingers and throw the barn off of her in a fit of rage. However, this might just be a simple matter of physics due to how large she is.
 * Immense Durability: Blue Diamond seems to be more durable than other gems as she was able to survive when the Crystal Gems literally threw everything they had at her, and when Lapis threw the barn on top of her and when her hand ship landed crashed on top of her and she came out without a scratch (while this would have likely poofed other gems). This is likely due to her sharing the same invulnerable nature as her gem, much as how Peridot's gem type gives her extreme durability.

Yellow Diamond
"Why can't you just let me grieve?" Due to their roles as the Gem matriarchs, Blue and Yellow Diamond treat each other with respect, considering themselves equals. However, Pink Diamond's shattering is a source of friction between them, as Yellow and Blue Diamond have been arguing for thousands of years over their different ways of coping with the loss of Pink Diamond. Despite their differing beliefs, they still care about each other, as when Yellow nearly broke down after singing "What's the use of feeling, Blue?", Blue comforted her by placing a hand on her back. Similarly, Yellow and Blue are holding each other when they enter the trial room, and Yellow places her hands on Blue's shoulders when she breaks down at the trial.

Their attitude toward legal matters suits their roles as overruling authority figures. Yellow Diamond is a militant, considering trials as pointless and would prefer unhesitating action while Blue Diamond prefers to hear every opinion possible to determine the best possible decision even through slow, lengthy processes. When Yellow Diamond is outraged by the fact that the defending Zircon accused one of the Diamonds of Pink Diamond's shattering, she poofs both of the Zircons, which makes Blue Diamond angry, yelling at her fellow Diamond "Can't you restrain yourself!?".

In "Reunited", when trying to explain he has Pink Diamond's gem to Yellow and Blue Diamond, Steven claims that Yellow, Blue, and Pink see/saw each other as family.

After discovering that Pink was never shattered, Blue and Yellow seem to have become slightly closer, as their differing ways of coping with Pink's death have become irrelevant. Blue encourages patience in Yellow, and Yellow comforts Blue when she becomes upset at the mention of White Diamond.

Pink Diamond
"Oh, Pink. I'm sorry... I'm so sorry... I should've done more. Yellow says it'll all be over soon. I wonder what you would think. This is your planet, after all. I still think it is." Blue Diamond describes her past relationship with Pink Diamond as very close and still grieves for her thousands of years after she believes Rose Quartz to have shattered her. In his dreams, Steven saw Pink Diamond's abandoned Palanquin where Blue Diamond knelt down and wept over her passing, which led him and Greg to seek out the location and find Blue Diamond there. Blue Diamond cares deeply about protecting Pink Diamond's legacy, causing her to take Greg to Pink Diamond's Zoo so that one more human can be saved before the Cluster destroys the Earth. Following Pink Diamond's shattering, Blue Diamond took over operations of the Zoo in an additional attempt to keep her memory alive, where she preserved all the remaining Rose Quartz gemstones in bubbles, contrary to Yellow Diamond's wishes, due to Pink Diamond's role in inventing the Gem type.

During the events of "The Trial", Blue Diamond reveals that she's been wondering how Rose Quartz was able to get past all of Pink Diamond's attendants and shatter her in the first place. Because of this, she asks Steven (who she believes is Rose) how he committed the act, and becomes distraught when he doesn't know; nothing adds up. Blue Diamond appears very interested by the idea of an authority figure shattering Pink Diamond and is completely shocked when the defending Zircon states that it could have been one of the other Diamonds.

Despite loving Pink in a familial way, Blue Diamond tended to disregard her opinions rather than acknowledge her as an equal in the Great Diamond Authority. It is shown in "Can't Go Back" that Blue treated Pink like a child in those circumstances, telling her to stop coming up with excuses and forbidding her from arguing back while at the same time reassuring her it will all be fine because of her status. When Pink Diamond made a plea to call off the colonization of Earth in order to preserve the lives of its natives, Blue Diamond had the Zoo built for her to preserve select specimens instead. Blue and Yellow Diamonds' stubborn refusal to halt colonization efforts eventually led to Pink Diamond herself responding with rebellion under the alias of Rose Quartz.

In "Reunited", when trying to explain he has Pink Diamond's gemstone to Yellow and Blue Diamond, Steven claims that Yellow, Blue, and Pink saw each other as family. After discovering Pink's true fate, Blue is extremely relieved to find out that Pink was never shattered.

In "Familiar", Blue notes that she always enjoyed Pink's games and parties. However, "Together Alone" shows that she is not above threatening Pink if the latter goes too far.

Steven Universe
"I'm so glad you're back, Steven. Steven: Y-you actually said my name. Steven. Steee-von." Even before she knew of his existence, Steven made an empathetic connection with Blue Diamond that allowed him to feel her grief as she mourned at the palanquin of Pink Diamond. This behavior may be the result of feedback between Steven's empathy and Blue Diamond's own pathokinesis. He also overhears her conversation with Yellow Diamond on how to cope with Pink Diamond's shattering, which made him feel even more sympathy for her.

Upon meeting Steven in "The Trial" when he is claiming to be Rose Quartz, she feels nothing but scorn and wants to inflict the worst punishment possible upon him. Despite this, however, she shows restraint and mercy, even going as far as to host a trial to gather the information on how "Rose" shattered Pink Diamond before his sentence. During the trial, Blue Diamond showed frustration and grief afterward when Steven incorrectly recounted Rose Quartz's crime and showed shock at the revelation of a Diamond possibly being responsible.

However, as of "Reunited", she is finally aware that Rose Quartz is actually Pink Diamond and was never shattered in the first place. During the aftermath, she shows a genuine display of affection towards him by nuzzling him and hugging him. She also supports his efforts to cure the Corrupted Gems and expresses concern for him when he is brought to White Diamond.

In "Familiar", she is delighted to see him again, noticing that he hasn't changed, and briefly manages to call him "Steven" before returning to calling him "Pink", remarking the former is a funny name.

In "Together Alone", she attempts to discourage Steven from allowing the Crystal Gems to his "Era 3" ball, but relents after he insists that they come.

Blue Pearl
Blue Diamond has her own Pearl, assumed to be her servant. Not much is known about her, in part due to her quiet nature, but in "Steven's Dream", she exhibits great loyalty and respect towards her Diamond and follows her every command, only speaking herself when addressed. She also introduces Blue Diamond in "The Trial". According to Blue Pearl, Blue Diamond lets her draw during court proceedings, something that she enjoys doing, which may indicate that Blue Diamond cares for her.

Sapphire
Sapphire was once an aristocratic member of Blue Diamond's court who was valued dearly for her ability to see into the future. She appeared to talk frequently with her, by Sapphire's words. When Blue Diamond sentenced Ruby to be shattered just for fusing with her, however, Sapphire immediately fled the scene with Ruby and terminated her relationship with Blue Diamond. After meeting again over 5,000 years later in "That Will Be All", Blue Diamond initially does not recognize Sapphire as the same one from the Cloud Arena. When Garnet refuses to attend Steven's ball in "Together Alone" Blue Diamond remarks that Sapphire has some sense.

Ruby
"I can't believe all that stuff about Blue Diamond being merciful! She's a shatterer! She yelled at Sapphire! She hates fusion a-and love!" To Blue Diamond, Ruby is nothing more than one of the common and insignificant soldiers under her command. When Ruby accidentally fuses with Sapphire, Blue Diamond immediately decides to shatter her gemstone as a punishment, even though the unexpected fusion saved Sapphire from the rebel attack. Like Sapphire, after meeting her again over 5,000 years later in "That Will Be All", Blue Diamond does not recognize Ruby as the one who fused with a member of her court.

Garnet
"Garnet? Does that call herself a Garnet?"

Blue Diamond dislikes Garnet due to being a fusion of two different types of gems. After seeing her form for the first time she was angry and disgusted at the fusion, sentencing one of her components to execution. After recognizing her again in "Reunited" she is shown to still hold a grudge against Garnet for disrupting her court and fights her along with the other Crystal Gems. However after finding out that Rose was Pink Diamond, Blue Diamond has stopped being openly hostile to Garnet, though she continues to show disdain for her.

In "Together Alone", Blue was surprised to hear Steven refer to Garnet by her name and arrogantly made fun of the idea, sarcastically asking if Steven expected Garnet to "enter with the Demantoids, the Hessonites, the Pyropes?".

Greg Universe
"I'm surprised that a human being is capable of understanding how I feel." Upon encountering Blue Diamond mourning by Pink Diamond's Palanquin, Greg approached her, and the two started talking. In their conversation, they were able to form a connection through their shared understanding of the loss of a loved one, with Blue Diamond and Greg missing Pink Diamond and Rose Quartz respectively (which, in an ironic twist of events, turned out to be the same person). However, Blue Diamond later resolved to kidnap Greg as a last resort to honor Pink Diamond's memory and took him away in her spaceship. Blue Diamond found it surprising that a human could not only understand her pain but also relate to it.

Holly Blue Agate
"This facility originally belonged to Pink Diamond and houses and staffs the otherwise useless Quartzes she produced on what was her colony. But Blue Diamond and her trusted Agate - that's me - have been maintaining this place since the dawn of Era 2." While the full extent of their relationship is unknown, it can be assumed that she trusts Holly Blue, as she gave her supervision over the Zoo. Since Blue treats anything related to Pink Diamond with utmost care, the fact that she trusted Holly Blue with the Zoo shows the amount of trust Blue Diamond has in her.

Lapis Lazuli
"A Lapis Lazuli? Does every Gem that comes in contact with this planet turn traitor?!" When Lapis arrived to help the Crystal Gems fight the Diamonds in "Reunited", Blue Diamond recognized her and acted with surprise over seeing Lapis Lazuli betraying Homeworld, before projecting her aura at her. She is then shocked by how her pathokinesis barely fazes Lapis, who chains her with her hydrokinesis.

White Diamond
"Yellow Diamond: Hmf! Good impression? We'll be lucky if she ever speaks to us again after this. Steven: But- The thing is, White can be... difficult." Blue Diamond seems to be afraid of White Diamond; she claims she is difficult to talk to and please. She reminisces to Steven of how much fun the four Diamonds used to have together in the days when Pink was still with them, indicating that White used to be closer to her fellow Diamonds than she is now.

White Pearl
"It's White's Pearl."

Connie Maheswaran
"You can bring your pearl of course, and your pet. Steven: Uh, pet? Connie: I think she means me."

Blue Diamond regards Connie, as a human, to be of little importance. She recognizes the sword Connie carries in "Reunited" and breaks it in anger. Later in "Together Alone", she assumes that Connie is Pink Diamond's "pet".

Stevonnie
"Pink, this is completely unacceptable! Unfuse or I'll make you!" Blue Diamond, along with Yellow Diamond, showed immense shock at Stevonnie, telling them to unfuse immediately. She was then seen crying in disappointment from them after Yellow poofed the Jades' fusion, Garnet and Opal.

Trivia

 * Blue Diamond is the first of the Diamonds to be seen on-screen in an episode of Steven Universe.
 * However, Blue Diamond was not the first of the Diamonds to be revealed in Steven Universe media as a whole. The extended theme song reveals Yellow Diamond.
 * Despite being a Diamond like Yellow Diamond, the cut of her gem does not exactly match her yellow counterpart, in contrast to most other Gems of the same type. However, since the two episodes they appear in were storyboarded by different members of the crew, their gemstones may only look different due to the differing art styles of the crew members, as they appear to be of the same design – a rhombus-shaped decahedron with a rhombus facet and four rectangular facets on the sides.
 * When she appears for the second time in "Steven's Dream", Blue Diamond's gemstone now bears a closer resemblance to Yellow Diamond's.
 * Rebecca Sugar has mentioned that blue-colored Gems are mainly diplomats.
 * Rebecca stated that Blue Diamond's character design is meant to look "ghostly" to get the feeling of her mourning, and draws much influence from Martha Graham's Lamentation ballet dance. Her face and hair designs are also inspired by Leiji Matsumoto's art, to make her come across as a "strange presence".
 * According to her mural, Blue Diamond ruled over nine planets when the Moon Base was built. It is unknown how many she currently rules.
 * Many Gems under Blue Diamond have similar gemstone designs (wider at the bottom, tapering to a point on top), reminiscent of a teardrop shape.
 * It seems that Blue Diamond wears a cloak while she is traveling and doesn't wear one when she is on Homeworld and her own places.
 * A notorious New Age scamming site, The Council of Love, utilizes the blue diamond as a symbol of the Virgin Mary, which may have inspired Blue Diamond's aesthetic similarities to the figure.
 * Blue diamonds represent peace, spirituality, and good health.
 * This is ironic, given that her lasting grief and mourning over Pink is far from an improvement to her well-being.

Cultural References

 * Blue Diamond's appearance and her throne appear to be heavily influenced by Indian and Muslim culture. Her clothing resembles that of a traditional Arab wedding dress, specifically a Henna dress.
 * The frame of her throne has carved geometrical designs for windows, which are a common design in many Indian temples and houses.
 * The largest blue diamond, the Hope Diamond, also originates from India. It is known notoriously for supposedly being cursed, depicted to bring forth misfortune to whoever attempts to wear it.

Gemstone
Blue Diamond Diamante Azul Blue Diamond Diamant Bleu Kék Gyémánt Diamante Blu Blauwe Diamant Niebieski Diament pt-br:Diamante Azul Diamantul Albastru Голубой Алмаз Mavi Elmas