How about Akumetsu?

In a political sense though but he has a reason why he did it before he snapped...

Equilibrium movie seems to fit your criteria, although the MC is badass from the very beginning and there is no lengthy power up moment.

You will never say the word "incident" like you did before 😀 Bang bang pewww

Thanks so much for all the suggestions, guys! I know I've already read most of the manga involving badass main characters (I make one of these threads periodically, but make sure to always change the criteria slightly in hopes of new suggestions. And it works!), but you guys are on a roll with suggestion stuff I haven't read/watched. I've read quite a few of the books already, but since books aren't on my list, you guys are still amazing. Anyway, thanks so much everyone! Keep those suggestions coming.

Does the walker choose the path, or the path the walker?