The world where suddenly 7 angels appeared from the sky and caused supernatural events, where some people suddenly got mysterious powers.

Summoned into an alternate world of Alayzard, Ousawa Akatsuki helps defeat the demon lord, brings harmony back into the world and, under the demon lord's last request, takes the demon's only daughter back into Akatsuki's own world. It turns out that being teleported into a different world is somewhat of a common occurrence back home. Those who return often come back with the power to use magic. So a worldwide organization, fearing people like Akatsuki, created Babel, a school to teach and keep tabs on the magic users. Akatsuki is able to bring the demon lord's only daughter into Babel as his sister, Ousawa Miu.

High school student Toujo Basara's life has taken a turn for the strange. Although hesitant about his father's sudden decision to remarry, he can't deny it comes with a couple perks—drop-dead gorgeous step-sisters…who also happen to be members of a demon clan! Mio Naruse is a Demon Lord and Maria Naruse her succubus servant. Chaos and passionate antics ensue as Basara gets acquainted with his new demonic siblings, trying to protect them from dangerous demon rivals and struggling to keep up with their lusty, devilish appetites.

"Hey, you said you wanted a little sister, right?" Highschool freshman, 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 would be getting remarried. He then departed overseas after bringing Basara two beautiful step-sisters. Things aren't as they seem in this series, as Basara discovers that his new "family" has a few secrets he's yet to unveil. Adaptation of the [Light Novel](https://www.novelupdates.com/series/shinmai-maou-no-keiyakusha/) series written by Uesu Tetsuto and with illustrations by Ookuma Nekosuke.