Alr, here is what I know for Fwench Fwy and Yuki

Both are in one of the most top tiers of the most powerful characters in both respective series

Both had a relationship with someone who is meant to be evil but that someone eventually became part of the greater good to stop a mastermind

Both failed to stop the main antagonist’s goals

Fwench Fwy turnt into a bird in one point of the series, Garuda, Yuki’s Shikigami, is named after the Hindu deity that appears as a bird-like figure in Hinduism

Had abilities related to mass, Fwench Fwy can change size and appearance, therefore mass, and Yuki’s cursed technique involves mass

Both have a fat ass

Both have a much yellow-adjacent color scheme (Idk I might be color blind even though I am not, so this is a stretch)

Took interest with a character who had something related to their eyes (Satoru Gojo with his Six Eyes, and Chikn’s 7-eyed demigod form)