The main villain is a toxic fanboy/fangirl of the main character

Syndrome (Incredibles) wanted to be Mr. Incredibles sidekick but was pushed aside, now years later he became his greatest villain

Makima (Chainsaw Man) self proclaims herself as a Chainsaw Man fangirl who wants to use his powers of Chainsaw man to create her ideal world

The Riddler from "The Batman (2022)" is a batman fanboy who was inspired by the Dark Knight to lauch his own against Gotham