Hey guys. I wonder if you know any mangas where the best friend or close friend of the protagonist truns into a major antagonist either (preferably) willingly or unwillingly. Also where he or she becomes a major or the main antagonist for the story or a major arc and not someone who is just used 2 or 3 chapters and than killed off/saved.
Something like Griffith from Berserk or Hirose from Alive TFE.
Any ideas would be appreciated. And no yaoi/shounen ai please.