Souichi seems to be a normal student, but he is actually an experienced bodyguard. One day, he was asked by his mother, who is also a bodyguard, to transfer into Reihou Gakuen to help her protect a certain girl at the school. Reihou Gakuen used to be a famous girls’ school, and even after turning co-ed, it is still predominantly full of girls. Moreover, he was surrounded by eccentric girls for some reason. One of them was the girl who he was supposed to protect, and she smugly said: “From now on, you are my ‘schwester’!” The girls seemed unapproachable at first, but he began to see another side of them as he got closer to them.