Itsuki Hashima is a popular, young novelist. However, he is obsessed with little sisters and his works seem to always include little sisters, so there’s some difficulty coming up with a new series. One day, his younger step-brother Chihiro and his colleagues, Hayato Fuwa, Nayuta Kani, and fellow college student, Miyako Shirakawa show up at his apartment. They enjoy dinner, drinks, and a game. That night, Nayuta makes advances towards Itsuki, but...

Nayuta and Miyako walk in on Itsuki, who was naked in front of the bathroom mirror, trying to act out the little sister character in his new volume. Itsuki is everything to Nayuta, and Miyako secretly has some feelings for Itsuki, but Nayuta also cherishes Miyako because she showed her compassion in her time of need. Nayuta invites Miyako to the hotel she’s staying at and immediately gets naked. She then asks Miyako to also get naked for some kind of research for her novel...

Chihiro starts working part time at Ashley’s office. Chihiro cleans Ashley’s whole office and then goes to take a bath and Ashley finds out Chihiro’s “secret.” Meanwhile, Itsuki heads to the zoo with Nayuta so he can do some research for his next book and they observe all the naked animals. He then goes to the aquarium with Chihiro and then takes Chihiro home in a taxi and...