The main character, Keisuke Tsukikawa, whose sister-in-law’s personality has split and has become two sisters, is accompanied by
his sisters Saki Tsukikawa and Saki (a split body of Saki) and his classmate Riri Manabe (succubus). I’m coming to the beach.
Saki, who knows for the first time that Kasuke and blood are not connected, considers Saki’s feelings that were sealed.
Saki and Kasuke are alone in the shade of a rock.
So Saki urges her to do her actions when Saki and her personality have changed, and Kasuke accepts Saki.
That night, Saki, Saki, and Riri attack Kasuke who takes an open-air bath.
Succubus who originally have strong sexual desire and Saki who is influenced by it and has a nasty nature urges her favorite Kasuke to seed.
Kasuke, who is at a loss if he cannot love the three in the same way, gives one answer to his smiling sisters who have not changed since he was a child.