High school student Aoi Aioi lives with her elder sister, Akane, after a tragic accident took their parents away 13 years ago. Because Akane has since been taking care of her single-handedly, Aoi wants to move to Tokyo after her graduation to relieve her sister's burden and pursue a musical career, inspired by Akane's ex-boyfriend Shinnosuke "Shinno" Kanamuro. Shinno was part of a band until he left for Tokyo to become a professional guitarist after the sisters' parents passed away, and he was never to be seen again.

Her Blue Sky

Unaired special of “Himouto! Umaru-chan” included with the manga’s tenth compiled volume.  Realizing it is Taihei's birthday, Umaru asks Nana for advice on what to do for him. Umaru decides to act like an ideal sister and spend time with Taihei, only to discover that he prefers her the way she is. Later, as the girls begin their summer vacation by going to a swimming pool, Umaru wonders if she should stop putting on an act in front of her friends and reveal that she, Komaru, and UMR are the same person. As Umaru becomes conflicted over what will happen if she tells everyone, her friends assure her that she doesn't need to reveal her secrets if it'd just make her suffer. Relieved by the support of her friends, Umaru makes the decision to continue hiding her secret.