Yuzawa Yuuki is a pessimist. He thinks that life is meaningless since everyone is going to die one day.

Before the Christmas he meets a mysterious "angel" girl Mika. She claims that she came to save Yuuki from his desperate state. He doubts her sanity but decides to play along. After that self-proclaimed "devils" appear. Some of them aim to claim Mika's life, others are here to tempt Yuuki.

Yuuki's long and unforgettable Christmas night begins.

[From vndbreview]