Variante - requiem for the world (Variante -ヴァリアンテ-?) is a Japanese horror manga by Ikura Sugimoto (the pen-name of Mao Kuon). The manga is divided into four volumes, each one having a cliffhanger that leads to the events in the next volume.
Hosho Aiko should be dead. To be precise, when she came back home that day she found that her entire family had been slaughtered by a monster, and the creature attacked her too; she was dead, but she awakes in a "secret" hospital. She has amnesia, but when a monster appears before her, she remembers everything, and her arm changes into a powerful weapon, very similar to that of the monster, and destroys him.
As soon as she recalls what has happened, she only thinks to die and reach her parents, but something inside her still wants to live. She'll learn that those monster are called Chimaira, and that her arm is made with the very same substance as the monsters (a Chimaira arm), so the people from the secret organization Atheos ask her to fight the monsters for them.
Unable to cope with that, she runs away to her best friend, but first terrorizes her when her arm kills her dog (on his own initiative), then she gets killed by a Chimaira, and Aiko can do nothing more than avenge her. More desperate than ever, she initially refuses to fight and she'd rather become a guinea pig, then, with Sudou's help, she understands how much she wants to live, and joins Atheos.
After joining Atheos, Aiko helps battle the chimeras, fighting her third one down in a sewer, where she is injured and had thought to have eaten it after Sudo comes to rescue her. After that battle, Aiko asks Kochigawa why Sudo is not afraid of her. Sudo answers Kochigawa later that of course he was afraid of her.
Script error In Jason Thompson's online appendix to Manga The Complete Guide, he regards the protagonist's "emo and paralyzed by doubt" nature as being due to the influence of Neon Genesis Evangelion on manga and anime.