Qiubai has traveled to a world where inner and outer worlds merge. Growing up, he's surrounded by characters he's "familiar" with. There's Akizuki Airi, Akizuki Marina, Shiina Chizuru, Mashiro Chisato, Hoshizuki Kaede, Hoshizuki Suzu, Nanao Akane... and his two younger sisters, Mikan Yuuki and Kasugano Sora, who live with him. Mikan is young, but capable, mature, and energetic, taking care of the housework daily, making her a worry-free existence. Sora is slightly older, but aloof and tsundere, with a slightly frail constitution. She stays at home every day, a worrying prospect. When Qiubai turns 18, the system officially activates! Kuze Akibai: What? Just coming of age, I have to become a male succubus in the inner and outer worlds? And I even have the ability to stop time!