really any character that gets fridged early on runs the risk of this. a dead lover, family member, etc will be hugely important to the protagonist and may drastically change their motivations in game, but there's often not much meat to the fridged character themselves, resulting in a lot of headcanon.

(putting aside the other problem, which is that these kinds of characters rarely get apped for any other reason than to join an existing cast and be that super important person to the other characters. i'm sure most of us have deliberately joined a cast at some point, but i'm always a little wary of very minor characters whose main defining features lie in their relationships to more well developed characters. apping a character, not because you're excited about the game or the character themselves, but because character x is going to shit themselves/fall all over character y who died tragically in canon and spurred all of x's subsequent development, rarely ends well.)