Its the night young Lucy snaps and turns homicidal after having to watch her puppy being killed.
BUT, before things get ugly, she finds herself and her dog in a huge arse lab being probed every which way. Said lab belongs to one Washu, and no matter how hard she tries, little Lucy can't escape the mad scientist's demonic technology. When all is said and done, little Lucy, the future Diclonius queen, is paid for her time and offered another life.
A few weeks later she ends up enrolling at UA under recommendation(after getting used to living on her own, buying things with money, etc...she has enough to last both herself and her dog, until she turns Pro Hero) where, instead of going berserk and threatening the planet, she'll train to become a hero.
And possibly, the next Symbol of Peace.
The most dangerous organism of the Elfen Lied universe must now grow up in the world of My Hero Academia, without any of the bad stuff which turned her into the queen of massacre.
How does Lucy do?