Siblings

Summary
Rumi asks Bossun how should she address Tsubaki since she and him are not related by blood. Bossun tells her to call Tsubaki, "onii-chan." Over at school, Bossun informs Tsubaki about Rumi's situation and tells Tsubaki to call Rumi like his little sister. Sasuke says that Rumi is not his sibling and he isn't interested, this makes the atmosphere between the two become awkward.

The next day, Bossun takes Rumi to see a movie with him, and the two bump into Tsubaki. Then, Akane calls Bossun to help her because she lost the house key. Bossun leaves Sasuke his student ID and suggests that Tsubaki and Rumi watch the movie together. Later that night, Tsubaki tries to walk Rumi home, and he manages to save Rumi from falling down the stairs. He mentions that he was alone throughout his childhood. Despite these sudden changes, Tsubaki states that he would like to have a little sister. Rumi is glad that they don't have to formal and calls Tsubaki, "onii-chan." At school, Bossun is amazed how Tsubaki and Rumi's relationship has improved.