The story takes place at an old mansion located in the basement. There is a big clock and a monster is sealed off inside. The clock is guarded by Kurogami family and Sigma, a successor, lives a peaceful life. But one day, the world loses everything. The world is in ruins, the monster covers the sky, and people disappear.... Only Sigma and Neon remain there. "Our past must have been rewritten." They transcend time and investigate the facts. However, they face cruel murders and unknown past along the way. What's happened to their world? A story now begins....
an extended description!