Oshino Ruka♀

A succubus who works as a caretaker of the school dormitory, Ruka was Kouichi's classmate when they were in high school and also his first love. Due to some circumstances, on the day when they were supposed to go on their first date, they were forced to be apart and had lost contact with each other since then. They reunited when Kouichi was brought to the village by Mami and Marin.

At the end of the second title, Ruka admits to Kouichi that she is still somewhat has feelings for him and accepts his offer to participate in the naughty lesson, becoming the heroine of the third and final title of the series.