I can't remember the name of the manga but I remember one of the main characters was able to like cut people in half with his kicks and he wasn't super smart. He ends up working for someone who looks like an old man but is later revealed to be a buff dude who had surgery done to have his face look like an old man. The only other scene I really remember is that a girl the main character liked was kidnapped along with another girl (spoilered because I think it's gross)
Spoiler (mouse over to view)
and the kidnappers like cut the nipples off one of the girls and there was like blood spewing everywhere.
If anyone is able to figure out the title thank you!