Gisou Honey Trap  

偽双ハニートラップ

A 15-year-old named Keiichirou Mishima lives with his mother until she suddenly travels to Paris to be reunited with her husband. She arranges for her son to stay at the mansion of her uncle Shirasaki, along with his two cousins Marie and Tomari. Although Keiichirou has previously met these cousins, he has almost completely forgotten why they now seem to dislike him.