Shadow mate ~小さな竜と適合者~

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.