Variante

Variante: Requiem for the world (-ヴァリアンテ-, Variante) is a horror manga series written and illustrated by Iqura Sugimoto. It is published by Kadokawa Shoten and collected into 4 tankōbon volumes. It is serialized in the Monthly Dragon Age in 2004. The manga was later licensed in North America by CMX on July 7, 2006.

Plot
The series follows Aiko Hosho, who wakes ups in a secret hospital. She has no recollection of what happened that night, until a monster showed up and her memories flood back. Her arm changed into a powerful weapon similar to the monster, a chimera arm.

The secret organization, Atheos asked her to help them fight off the chimeras. An accident happened that led Aiko to understand how much she wants to live, and decided to join Atheos, in order to find her place.

Other Sources

 * Wikipedia
 * Mangaupdate
 * MyAnimeList
 * MyAnimeList