In superfamily Peter bullied fanfiction, a frequent theme is transformation. Peter could start off as a bully but then something in the superfamily dynamic, like a new member joining or a major event, causes him to transform into a better person. Another common theme is the impact on the family unit. His bullying behavior might strain relationships within the superfamily, and the fanfiction could explore how they deal with it, whether it's through confrontation, forgiveness, or some other means.
Well, often there's a theme of growth. Peter, through his bullying phase, might learn about empathy. In this kind of fanfiction, the writers might show how his actions have consequences not just for the victim but also for himself within the superfamily. And there could be a theme of secrecy too. Maybe Peter tries to hide his bullying behavior from the rest of the superfamily at first.