For me, the orphanage episode of Elfen Lied was the most amateurish attempt at a backstory. If you want a good villain backstory, don't rely on shock value or use the cheap and cowardly tactic of making children into villains. The only reason that trope exists is to make older people feel good about themselves. Not to mention that it sounds like a sob story that real criminals use to try and manipulate people into feeling sorry for them.
Or perhaps deconstruct those types of origins like I did with a character I wrote. He's a humanoid cat who was once a normal cat of an ordinary girl, until he was beaten to death by a bully. But he was ressurected as a humanoid and wants revenge on the bully... or so he thinks. It turns out he was never a cat and is actually the bully, mutated into a humanoid cat, lost his memory, got fake ones, and you can already taste the twist, can't you?
