Lucy's horns made her a target for cruelty and isolation. A small puppy she kept as a secret was her only friend. Targeted by a particular group of bullies, ring-lead by Tomoo, she seemingly gains a friend and ally in one of the other girls. Whether tricked or a liar herself, the girl reveals the puppy's existence to the bullies, and they kill it before the eyes of the girl who will become Lucy. Undergoing a rage-filled psychotic break, Lucy unleashes her hidden powers for the first time and kills the four children. As she buries her puppy, a despondent Lucy first meets Kouta, staying in the Kamakura area with his family. Despite her mistrust, a short period together and restrictions on his ability to visit her, the two quickly form a bond and friendship that partially reawakens her spirit. Although her disconnection with humanity is still profound, and she is killing whole families merely to obtain a place to stay for the night. When their last day together comes, he tells an innocent lie meant to spare her feelings, a lie that she bitterly learns the truth of, again sinking into despair and rage. Attending a festival with Yuka and his younger sister, Kanae, he is horrified to hear that a horned girl killed over a dozen people there, an event that spurs his father to decide to go home in Hokkaido. Aboard the train ride home, Kouta thinks of both his new friend and Yuka, who also did not wish to see him leave, and argues with Kanae, feeling her account of the horned girl is simply wrong. Lucy emerges from hiding, with Kanae again insisting that her story is true, raising Kouta's ire. In a horrific moment, Lucy kills Kouta's family and also vows to kill Yuka. A heartsick Kouta demands she stop killing, and his sadness is more than enough to make her realize that she has driven him away forever.
This horrific incident explains his present-day amnesia. In the present, Lucy attempts to leave for good, but Kouta stops her. She also tries to confess her old crime to him, only to have the guilt and shame overwhelm her and force a reversion to Nyu. Joyously, the childlike Nyu embraces him amidst some anxious moments with Yuka.