I've thought of an idea for a "Steven Universe" movie where Rose Quartz returns at the end of the movie. The homeworld gems invade the Earth with a total of 500 gems, and they manage to capture the bubbled gems in the temple, release them and force the corrupted gems to fight against the Crystal Gems. By the time the movie takes place, Lapis Lazuli and Jasper have unfused, Jasper manages to have returned to homeworld to help with the new Earth invasion, Peridot has earned redemption and she and lapis have joined the Crystal Gems.
The Crystal Gems manage to get ahold of the bubbled cluster gems before Homeworld could. The homeworld gems divide into groups of 10 gems in each group and spread out over the Earth to start taking control of its smaller towns first. Because Lapis has a powerful ability to control water and Steven is the only one who can access the weapons in Rose's secret armory, Lapis and Steven take the bubbled cluster gems and are sent to Rose's secret armory.
Lapis and Steven are tasked with guarding the armory and reactivating Steven's healing powers so that he can heal the cluster gems so they can separate and reform back into their original selves and help fight the homeworld gems once more. The other Crystal Gems, Pearl, Garnet, Amethyst and Peridot try to take out the divided homeworld gem groups. Peridot is helping them because she has been on Homeworld more recently than the rest of the other Crystal Gems and because she understands Homeworlds new technology better so she can help the Crystal Gems disable it.
The crystal gems are able to take out 5 homeworld groups before it becomes way too much for them to handle. Pearl, Garnet, Amethyst and Peridot return to Rose's secret Armory to discover that Steven and Lapis have had no progress in reactivating Steven's healing ability. When the gems tell Steven and Lapis about how they were only able to take out a few homeworld gem groups before they realized they couldn't beat all of the homeworld gem groups, both Steven and Lapis become saddened and angered by the news.
It seems like there is no hope for the crystal gems to stop the homeworld gems. Steven starts to cry tears of hopelessness. He talks about how the world and people that he love will be "lost" forever soon and how that makes him sad and angry because it seems like there is nothing he can do about it.
Steven's sadness and anger becomes so strong that it reactivates his healing power and he heals every cluster gem in Rose's secret armory, turning all of them back into their crystal gem selves; which causes Steven to stop crying and start smiling. With all of the cluster gems(now crystal gems again) healed, the crystal gems start to gain hope. When the crystal gems notice 50 homeworld gems coming towards Rose's secret armory, all of the crystal gems decide it's time for fusion.
Three mega gem fusions are formed. The three mega gem fusions are Red Hope Diamond, Blue Hope Diamond and Green Hope Diamond. Pearl, Garnet, Amethyst, Peridot, Lapis Lazuli and Steven are fused into Red Hope Diamond.
The three mega gem fusions defeat the 50 homeworld gems that try to attack Rose's secret armory and travel the earth to defeat the remaining homeworld gems. After defeating 380 homeworld gems, the three mega gem fusions learn the remaining homeworld gems are at Beach City with the corrupted gems that the homeworld gems are forcing to aid them. It's a tough battle because the 20 homeworld gems at Beach City are the strongest homeworld gems that came with the invasion.
When things appear to be getting turned in homeworld's favor, Red Hope Diamond uses their(Steven's) healing ability to heal the corrupted gems. After being turned back to normal, the healed gems help the three mega gem fusions defeat the remaining homeworld gems. After being beaten, all of the homeworld gems that invaded earth flee back to homeworld.
With all of the homeworld gems gone, the three mega gem fusions unfuse. After the three mega gems unfuse, all of the crystal gems, the healed corrupted gems, all of the citizens of Beach City, Connie's parents and Connie all cheer because of the victory. Suddenly the gem Goddess Jewel appears infront of Steven. Jewel congradulates Steven, stating that he is a brave gem and that it was his healing power that helped the crystal gems win the 2nd gem homeworld invasion.
After Steven thanks Jewel for congradulating him, Jewel tells Steven that she has the power to grant one wish to any gem that she feels is worthy and she believes that Steven is the one who is worthy of the wish. Steven is absolutely thrilled. Jewel warns Steven that she can only ever grant one wish and that she couldn't fix Steven's wish if he makes a mistake and that she will never be able to grant a wish to any gem ever again.
Steven takes a few seconds to think about what it is that he wants the most in the world. Steven decides what it is he wants to wish for. Steven tells Jewel that he wishes that both he and his mom(Rose Quartz) could both exist at the same time without him and Rose needing to be connected at the gem and Rose having her own rose quartz gem. Everyone around Steven is surprised by his wish, thinking it can't happen, but Jewel tells Steven that she can grant his wish, but it will take up a lot of her power, to everyones surprise.
Jewel raises her staff to the air and a bright white flash emits from her staff and she disappears. After Jewel vanishes, a small bright pink colored orb appears where Jewel was and starts to take Rose Quartz's shape. Rose emerges from the light pink light.
All of the crystal gems, Steven and Greg start crying tears of joy as they all talk about how their all happy to see Rose again. Rose sees Steven and Greg and runs to them and the three share their first ever family hug with all of the Beach City citizens watching them. The movie ends with sentimental music playing while a star shaped iris closes in on the family.