Himitsu – Kuro no Chikai

Based on the popular Vocaloid song . Rin, a young angel (presumed female, but angels don’t have clear genders) falls in love with a young human girl, Miku. However, their love is considered taboo, and so, Rin makes a deal with the devil to be reborn as the human boy, Len, in order to be with Miku. However, their happiness together is short-lived, and even that soon ends in tragedy. — Description from novelcodex.orgFull novel: Himitsu – Kuro no Chikai — read the rest free on N​o⁠v​e⁠l​C⁠o​d⁠e​x⁠.​o⁠r​g⁠