HHG Megami no Shuuen

Kyuushirou wakes with no memories — not even his name, until his sister Hikari tells him. At their school, he meets three exceptional girls: Nadeshiko, the most saintly student; Fiana, heir to the saintess's knighthood; and Sally, the only person in the world born with three gifts. Kyuushirou has a premonition: if any one of them becomes the saintess, the world will be destroyed. A mysterious figure tells him his very existence will cause the world to collapse. Then his own hidden gift awakens — and he finds a library he has somehow been in before.