After Yame accepted his request to go out with her, Junichi is in a bit of a daze, not sure whether it’s all a prank or not, considering what he believes to be the logical fallacy of a cute gal dating the likes of him. His loser friends commit to standing by him come what may, only to immediately turn their backs on him when he receives a sexy selfie from Yame.
Despite this, Shinpei still offers advice to Junichi: take Yame to karaoke, which is how popular kids “get a room” for sex. He elaborates on the process with his “Karaoke XXX Rule”, before “dying” from exasperation that karaoke parlors have become indistinguishable from dens of ill repute.
Later that morning, Yame proves she’s not messing around by announcing to the entire class that she’s dating Junichi, then fielding questions. Both Kashii Yui and his “little sister” are dumbfounded. Junichi tries to ask her out to karaoke, but never finds the right opportunity until she asks him out after school to that very thing.
Corrupted by Shinpei’s overblown theory about karaoke parlors (which seems to be confirmed by a sign), Junichi is initially weary of their date, but once he sees how much fun Yame is having, he stops overthinking things and has fun himself. To his surprise, she even knows anime songs; the only kind he can sing.
But after Shinpei’s three tenets of the Karaoke XXX Rule are fulfilled (Yame singing a suggestive song; the two singing a duet; Yame removing her sweater), Junichi re-enters his head for a conference with all his various alter-egos, including ‘Good’, ‘Pessimistic’, ‘Horny’, and ‘Cool’, with ‘Cool” him eventually convincing the others that if he’s a true man, he’ll give her a kiss before moving on to sex.
Junichi tries to kiss Yame, only for her to point out an errant hair sticking out of his nose and excuse herself. Out in the hall, she regains her composure, certain Junichi just tried to kiss her. Far from the easy girl for whom sex is no big deal Shinpei, his friends, and Junichi himself believe her to be, Yame isn’t the kind of girl to even kiss someone so easily. She’s more like Junichi than he presently realizes.
Hopefully he’ll find this out in time, and stop interacting with Yame with misconceptions about who and what she is, just as she seems to be embracing him for who he is, not assigning a silly label. As for Yame’s friend Ranko, it appears we’ll soon learn how she feels about this new boyfriend.