Haiiro no Kisetsu, Hakoniwa de

This is the story of girls who are compelled by immortality. These girls gather in a boarding school on a solitary island in the distant seas. The girls who possess the inability to age live and die by the experiments done there, with immortality as the aim. With nothing to rely on in an institution where immortality is worshiped, transfer student Nagami Chihaya enters the scene. Rejecting perpetual youth, she yearns to be an adult. With her transfer, the fates of the students at the institution begin to move tremendously.

Note: Chapter count includes 2 extras.