The Testament of Sister New Devil (2015)

Basara Toujou’s life takes a chaotic turn when his father unexpectedly brings two captivating girls into their home – fiery redhead Mio and petite silver-haired Maria – declaring them his new sisters. What begins as an awkward introduction quickly spirals into something far more extraordinary, because these seemingly ordinary girls are anything but. They're demons: Mio is the last daughter of a legendary Demon Lord, and Maria her devoted succubus attendant. Forced to confront a past he thought long buried, Basara reveals his own history as a former "Hero," destined to fight against demonic forces. Yet, unexpectedly finding himself drawn to his new sisters, he chooses a different path – one of protection rather than conflict. He vows to shield them from danger, even forging an unusual master-servant bond with Mio to keep her safe. Now caught between the watchful eyes of his former Hero allies and the looming threat of vengeful demons, Basara faces an impossible task: safeguarding his unconventional family. And as he struggles to navigate this precarious existence, a dark secret from his own past threatens to resurface and shatter everything he holds dear.

Basara Toujou carries a heavy burden. As the stepbrother to the captivatingly powerful demonic sisters, Mio and Maria Naruse, he’s fiercely dedicated to their safety – shielding them from predatory demons eager to exploit Mio's unique abilities. But his protective duties are complicated by escalating political unrest brewing within the demon realm itself. When Mio receives a summons demanding her presence in that volatile world, she and her companions venture into danger despite Basara's concerns. Now deep within enemy territory, Basara finds himself facing an unprecedented challenge: to become stronger, unlocking hidden potential through unexpected experiences, all for the sake of safeguarding those he loves.