When "Cynthia," a young girl held captive in a mysterious laboratory, woke up, she felt something strange in her body.

Her body was possessed by Belial, a vicious life form created by the institute.

The taciturn and calm Cynthia, and the maniacal and depressing Belial.

The two seem incompatible with each other, but both have a desire to get out of the institute.

In the end, they use each other in their relationship to escape from the institute.