This anime is great for you gore freaks, its about a mutant girl named Lucy/Nyu, a boy named Kouta, and his cousin Yuka. Lucy is a mutant which this organization keeps her locked up, they test on and torture these mutants. the mutants have horns and invisible hands and if they touch you without killing you, they impregnate you. The mutant children can't actually reproduce which means the end of the human race, that's why this organization was built.
First episode Lucy escapes but gets shot in the head, she wakes on the beach where Kouta and Yuka find her. Lucy forgets herself and can only say Nyu and has a total persona change. Kouta and Yuka call her Nyu. You find out later Kouta's sister dies from a sickness, but the truth is Lucy killed her when Kouta and her were friends, and has repressed his memory.
The main story is pretty much, the organization tries to find Lucy but since she forgot who she was she hasn't killed. Kouta slowly remembers what happens but still protects Lucy/Nyu. which disturbs me is you can tell Yuka gets jealous of Nyu, and shes is his cousin. There's lots of blood and gore, a story of friendship and love. the anime is only 13 episodes I'd consider it a rental, and there is a lot of unanswered things. for you lady's a warning there is a little dog that gets brutally killed when Lucy is a child which drives her crazy. If you end up loving the series i suggest reading the manga because it goes further in the story.