The Testament of Sister New Devil

Sinopsis

High school student Basara Toujou's life takes an unexpected turn when his father remarries and introduces him to two new stepsisters, Mio and Maria. Soon after, his father leaves them to go abroad. Basara quickly discovers that his new sisters are not ordinary girls: Mio is the daughter of the former Demon Lord, and Maria is a succubus who serves her. Basara, however, has a secret of his own, being a descendant of a clan of demon-fighting heroes. To protect Mio from other demons and heroes, Basara forms a master-servant contract with her, though an accidental reversal makes him the master instead.