Responses
I don’t think that’s a fair comparison. Many animes don’t have one side of the couple raising the other. And when they do, it gets called out as weird too (i.e. Usagi Drop is considered to have one of the worst endings).
That being said, I don’t think age gap is a problem. It’s just weird that she’s his guardian, essentially acting as his mother.
She's a hundred years old, no matter what she'd continue to age and remain young and beautiful physically as long as she's not killed plus she's not a human as long as the she falls for the ml when he becomes an adult then it's okay there are literally many animes out there that one of the lead is a hundred or thousand years older than the other