Young man Ryuji works hard to support his younger sister, Rin. One day, he is killed by an evil spirit and becomes an evil spirit himself.

Before Ryuji, who is no longer human, appears Sylphid, a wind spirit who should naturally be incompatible with evil spirits.

Seeing Ryuji, Sylphid makes him a certain proposal…?

A forbidden-contract dark fantasy where two beings that should never have crossed paths—spirits and evil spirits—join hands!