A Sister's All You Need.

Itsuki Hashima, a popular young novelist whose work always includes little sisters, is having difficulty coming up with a new series; his younger step-brother Chihiro and some of his colleagues come over for dinner, drinks, and games.

Nayuta and Miyako walk in on Itsuki naked; he ends up embarrassing himself and complicating the trio's relationship.

Itsuki, Nayuta, and Miyako have a hard time dealing with the cold and head down to Okinawa; they visit a remote island so Itsuki can do some research; Nayuta decides to flail around naked in the water; Miyako is awed by what she's seeing.

Nayuta, Miyako and Haruto gather at Itsuki's room for Valentine's Day, and Haruto tries to show off his friendship with Itsuki again; Toki arrives with the chocolates that fans had sent to them.

Itsuki is nearing his final deadline for volume 5 and flees from his editor; Itsuki manages to escape when he runs into Setsuna and they both go to a hot springs; Setsuna felt like he was in a slump and wanted to get some inspiration.

Itsuki has a meeting with Kaiko Mikuniyama, the manga artist who will be doing the manga version of "Mahou Academy;" she looks very refined, which makes Itsuki nervous, but apparently she loves little sisters as much as he does.