I am interested in reading some manga where a "good guy" (not necessarily the protagonist, can also be a side character) becomes a villain. Oftentimes in manga, I see a lot of villains joining the good guys, so a reverse situation would be interesting to me.

It would be nice if the good character actually became evil voluntarily (ie. they genuinely agreed with the villains' motives).

I would like to avoid scenarios where the character was "good all along" (ie. they only joined the villains to spy on them), or they were "bad all along" (ie. they were spying on the good guys and now they're going back to report to their boss).

If I've made a thread in the "I'm Looking For..." forum, I am only interested in Japanese manga. I am not interested in non-Japanese media at this time.

Mein Kampf :^)

Seriously, though, that's a big plot point in Devilman, Metropolis and The Sky Crawlers (Novel) (If you follow the franchise) sort-of has that, Ningyohime no Gomen ne Gohan, Übel Blatt probably (But, it's been a while since I read it), Death Note has some of that, and Mobile Suit Gundam (Especially depending on your views on the conflict). However, I'm a little confused by what you mean when you say, "they genuinely agreed with the villains' motives". I assume that you mean that the "villains" are still legit bad guys, correct?

Also, if you want to look outside of manga, there DC's Kingdom Come and Injustice comics, and (Unironically) majority of Marvel's current catalog.

[img]http://www.dragonflycave.com/wpay/mew.gif[/img]

You could try X, also found under X/1999, by Clamp. That has a bit of what you’re looking for I think. The problem is that is doesn’t really have a good ending because it was put on hiatus and discontinued. It’s a good story, but that’s something to keep in mind if you start it.

You probably have read this since it's pretty famous but I'll just try to recommend it 🙂

Noragami

The current arc has "from good to evil" vibes.

the process is making me depressed every month since the mangaka really took her time to 'torture' us with the dilemma until that particular person becomes evil (sadly) TwT