Harame ~Seishi o Hoshigaru Midara na Oshiego~

The protagonist, Ayano Taiki is a physics teacher at a high school. In school, he also acts as an advisor for the Astronomy Club which is a club consisting of only two members, sisters Aimi and Yumeno. He is living a peaceful and fulfilling life. One day in July, Taiki is invited by the sisters to come with them to have a "training camp" in their home village they are returning to for summer vacations. Since he has no parents or relatives and as such, nothing to do, he gladly takes the sisters' invitation When summer vacations start, he arrives at the countryside where the sisters wait, there he meets their cousins Saki and Chieri and receives a warm welcome. This will be a great vacation, is what Taiki thought... But what awaited him, were quickly-passing days full of obscenity.