The Testament of Sister New Devil

Basara Tōjō met his two cute little sisters, Mio Naruse and Maria Naruse. The two sisters revealed themselves as a member of the demon clan and Basara as a member of hero clan, demon clan’s enemy, and is not related by family. Mio is the future Demon Lord and since Mio’s power is not fully awakened, Basara will protect her from the demons who are after the power she inherited from her deceased father, Demon Lord Wilbert.

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“Hey, you said you wanted a little sister, right?” First year highschool student, Toujo Basara, was suddenly asked by his father and fell into a state of panic. On top of that, the eccentric father told him he will be getting remarried.
He then departed overseas after bringing Basara two beautiful step-sisters. But Mio and Maria’s true forms are actually the newbie Demon Lord and a succubus!? Basara was almost entered into a master and servant contract with Mio, but a “reversed” contract was formed by mistake, and Basara is now the master!? Moreover, Basara is being hit by one ecchi situation after another due to the contract, but Mio’s life is being pursued by other demon tribes and hero tribes! The most powerful contractor’s desire action drama begins!

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The “rather risque battle action” story centers around Basara Tojo, a first-year high school student who is flustered by a sudden question by his eccentric father, “Hey, didn’t you used to say you wanted a little sister?” Plus, his father announces that he is getting remarried. His father brings over two beautiful step-sisters, but then embarks on an overseas trip. However, the two sisters Mio and Maria Naruse are actually a novice devil and succubus. Basara almost ends up forming a dangerous servant and master contract with them, but due to an error, the contract becomes reversed, and Basara becomes the master instead. To add to things, erotic situations continuously start to happen in Basara’s life. However, it turns out Mio is having her life targeted by other monsters and heroes. And so, the “desire/action” tale of the strongest contractor begins.