Besides Steven, the main characters could include the villains he's faced in the past. Now that he's a girl, they might underestimate him or treat him differently. His father Greg could also play a big role. Greg might be a bit shocked at first but then would be super supportive, trying to understand what his 'new' child is going through. And there could be new characters introduced, like other girls in the town who become friends with Steven and help him adapt to the female world.
Well, it could be about Steven having some sort of magical or scientific accident that turns him into a girl. Then he has to deal with the new body, different social expectations, and how his friends and family react to this big change.
Perhaps she's a time - traveler from a future where the events in Steven's world have led to some big changes. She could be on a mission to prevent a certain catastrophe from happening, and her presence in Steven's time is a crucial part of that plan. She might have knowledge of future events and technologies that seem strange to Steven and the others.
Pearl, Garnet and Amethyst would surely be main characters. They were probably waiting anxiously for Steven's return. Once he is back, they could help him readjust to life at home. They might also assist him in dealing with any post - traumatic stress or new challenges that emerged from the Grem war.
Ichigo and Steven would be obvious choices. Ichigo is the main protagonist in Bleach, strong - willed and with great power. Steven, on the other hand, is kind - hearted and has a unique way of looking at the world. Their different personalities could lead to some interesting interactions. They could start off as strangers in a new combined universe and gradually become friends as they face common enemies or challenges.
If it was a crossover with "She - Ra and the Princesses of Power", Adora could be a main character. Her strong leadership and the power of She - Ra would be an interesting contrast to Steven's more laid - back leadership style. Together, they could fight against a common enemy that threatens both their worlds.
Lapis Lazuli could be a great addition. She has a complex relationship with Peridot, and her presence could add some drama and depth. For example, she might be initially suspicious of Steven and Peridot's friendship, thinking that Steven is influencing Peridot too much. But over time, she could come to see the positive aspects of their bond.
A love interest who breaks the girl's heart can also be a main character. His actions, like cheating on her or suddenly leaving her without an explanation, can be the catalyst for her transformation into an evil character. Then the story could revolve around her trying to get back at him in devious ways.
Perhaps the fanfiction could start with Steven having a strange dream about Pink Diamond. When he wakes up, he starts to notice small changes in himself, like his gem glowing pink more often or having strange new abilities. As he becomes more and more like Pink Diamond, he realizes that there is a connection between his mother and himself that he never fully understood. He then embarks on a journey to discover the truth about his transformation, along the way facing challenges from both the Homeworld and Earth - based gems who are either afraid of or intrigued by his new form.
It could be a new villain that has emerged. This villain might have some sort of vendetta against Steven specifically, perhaps because of his unique powers or his role in the gem world.
Well, clearly Steven and Connie are the main characters. They are the focus of the fanfiction.