A Plot where MC is tortured either physically or mentally (like killing/raping HIS loved ones) then he turns into a flipping psychopath or simply a lunatic with a cool head that can do anything for revenge and has no morals like 'Tower of Karma', I don't really like novels like 'Death Mage' for the reason of author making the tortured MC a anti hero one to a white knight that does good deed and chasing skirts talking about breast size of his harem etc ~
I've never read either of both, but maybe something like Youjo Senki and/or To Deprive a Deprived Person