Above Skin Love Circumstances

Hada no Ue no Renai Jijou
肌の上の恋愛情

Sequel

manga

Humans keep monsters as slaves for fighting and protection, but there is one, Zai who refuses to fight. Zai is special since he can use magic by creating spells with his songs, but he refuses to sing too... will he, for his master? (Source: Aarinfantasy)