http://www.mangago.zone/read-manga/the_hero_who_seeks_revenge_shall_exterminate_with_darkness/
Pretty obvious choice but only one that comes to mind
vinland saga
Im reading that one already, but u didn't realize it had been updated jdidjfisjf thank u
Already in the process of reading
Sorry ment *i didnt realize *
You could also try like:
- Pumpkin Night ( or any other works by the author )
- Akumetsu (doesn't really go insane though)
Other mangas revolving around revenge topic:
- Tokyo Revengers
- Blade of the Immortal
Nidome no Yuusha wa Fukushuu no Michi wo Warai Ayumu
Dungeon Seeker
Chand Ra Has (not really insane)
Aka Akatoretachi No Monogatari (this may even be more graphic than The Hero Who Seeks Revenge Shall Exterminate With Darkness)
Kinda bored but uh any good manga where the MC goes crazy like for revenge or in order to survive. Something that satisfying if that makes sense. Horror related is welcomed