Manga 11 Eyes

Satsuki Kakeru lost his sister by suicide and has been living a dull life ever since then. One day, he is transported into a bizarre world Red Night along with his friend Minase Yuka and six other classmates. In order to survive and escape from Red Night, they must defeat six black knights in order to return home. Adaptation of the 11eyes -Tsumi to Batsu to Aganai no Shoujo- adult PC game from developer Lass.