Episode 6: My Little Sister Can't Bring Her Boyfriend Home

The boy is introduced to be Kouki Mikagami, a designer from Misaki's company who, to Kirino's surprise, is also an otaku. Later, after Kyosuke explains the 'fake date' scenario to Ayase and asks her opinion on whether Kirino has a boyfriend, things get tense at the after-party when Kirino witnesses Ruri assumedly confessing to Kyosuke. Irritated, Kirino announces that Kouki is her boyfriend, pushing Ruri to leave and angering Kyosuke with her remarks. Later, Kyosuke becomes irritated when Kirino invites Kouki to their house, receiving an angered slap from her when he shows his distaste. After speaking with a drunken Daisuke, Kyosuke grovels before Kirino, explaining his honest feelings and stating he won't allow Kirino to date Kouki until he proves himself worthy. Kirino eventually breaks down and reveals she lied about dating Kouki because she was jealous of Kyosuke and Ruri, with Kouki agreeing to pretend to be her boyfriend. As the two siblings make up and decide to redo the party, Ruri finally asks Kyosuke to go out with her.