who are those on the second story?

They are all characters from a game called Genshin Impact

I'm not really sure but they look like the characters from honkai: star rail.

and then the third couple's from ZZZ. also a game.

yeah I can't figure out who exactly

Phainon x Caelus with impostor

who's the impostor?

Maybe flame reaver? XD

same hair and everything though TT but yknow for my peace of mind, that will do haha