Looking for a manga

Ok so the main character trying to get revenge for his parents? (Kinda vague on this it was a while ago that I read this) he trains to get stronger and gets a job in a morgue so he can kill people. On the last day of school he decides he no longer has to hide his strength and beats up the dudes who were bullying him. He later meets an old dude who decides to train him properly for killing and shit, I can’t remember what it’s called but I’ve been looking for it for ages. ┗( T﹏T )┛if you know it please tell me