From Elfen Lied. Cosplayer is Neliiell.
"I was born to put an end to Human life." (Real name Kaede) is the main character, protagonist and anti-heroine/anti-villainess of the Elfen Lied series. The so-called 'Queen' Diclonius, Lucy (also known as Kaede and Nyu) was an individual difficult to pin down by any standard "good or evil" social mores. She was both ruthlessly tormented and was a sadistic tormentor to others, driven to a mental break at an early age by the cruelty that surrounded her. Though she never expected to receive love and acceptance from others, occasionally she got the chance to see such things are indeed possible for someone like her to obtain. Her great love was Kouta, a boy she met when they were children and again when they were young adults. (elfen-lied.wikia.com)