Passions of Xanxor

"Passions of Xanxor" is a book owned by Greg Universe.

"Maximum Capacity"
It was seen in a box of books belonging to Greg Universe that his son found. Greg examined the books and then took "Passions of Xanxor", saying he would let Steven look at it in a few years, when he gets older.

Trivia

 * It is most likely a romance novel based on the cover art, the name, and Greg blushing and snatching it away from Steven.
 * The cover image, with a male human apparently falling for a larger/taller female alien, mirrors the relationship between Rose and Greg.
 * The cover image is also a parody of covers of real-life romance novels, albeit with the roles reversed: the man is the "damsel in distress" being held in the arms of the heroic female alien warrior.