Animes with similar plots o subplots

Mangas too. Come up with as many as te can. Here's an example:

*The original Yu-Gi-Oh (1st manga, season 0).
*DNAngel.
*DNA2.

Plot: A wimpy guy likes this one girl, but she only thinks of him as a friend. One giorno another soul possesses his body whenever his stress is high, this comes off as an alternate badass personality. The girl falls for the badass half, at first thinking them to be 2 different people. The boy's goal is to kick culo & man up, the girl's goal is to dibattito over which personality she likes the most.