Animes with similar plots ou subplots

Mangas too. Come up with as many as toi 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 jour 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 cul, ass & man up, the girl's goal is to débats over which personality she likes the most.