Akitsuki Kouzou

The protagonist. A researcher who managed to create an aphrodisiac while experimenting on hormone secretion. He often gets called to teach at the school his step daughters attend.

After an accident where he was exposed to certain chemicals he became sexually impotent for a while, but regains it after seeing Airi and Marina. Soon after this he realized that he only gets aroused by younger girls, and he decides to marry Airi and Marina's mother in order to get closer to them.