strade

He is very commanding and forceful, and does not have any pity towards anyone. Coming from a mostly unknown background, it can be implied that Strade has a number of psychological issues and fascinations. He is charismatic, a trait which many find very compelling. It can be implied that this trait, that many killers like him share, is his main device in luring victims.

As for his tendencies, Strade is a by the book definition of a sexual sadist. This implying he finds sexual arousal in making others suffer, which can also be seen in a number of his endings. This factor is one of the reasons the dripping red heart is achievable for his character and his alone.

You can go as far as to suggest Sociopathy, which may indeed be the case. Like a Sociopath, he has a very small field of empathy. However hard it may be for Strade to feel for others it is expressed in a singular route where he takes pity on you and keeps you for his own, as he has done before. So it isn't improbable to suggest his conscience is relevant, albeit hard to achieve.