"New toys are mine to play with first."
Gonna be completely frank: If I were writing this kind of story, I would've had a single panel of still silence right after Kuroiwa's forced-out confirmation, followed immediately by the same panel but with the guy abruptly standing up. He then silently picks up his things, slams his share of the bill on the table, say he's leaving when the older sister confusedly asks what he's doing, and turns around, then pause, and say something along the lines of the following:
"Oh also, two things. One: I'm not a toy for someone to play with; and two, even if I were, I wouldn't want to be anywhere near the filthy hands of such a black-hearted bitch. Goodbye."
Then he proceeds to storm off, pulling a stunned Kuroiwa by the wrist behind him and leaving the stunlocked and scandalized older sister in the dust.
Sorry, but this woman's behavior has gotten on my nerves big time. I wasn't expecting one of the major female characters in this series - even if a supporting one rather than a protagonist - to be so blatantly
villainous in characterization. It's almost making a part of me wonder if this she's not faking being the Big Bad Older Sister on a whim, and Kuroiwa noticed immediately when she arrived and is playing along to see what her not-boyfriend is gonna do. Or hell, maybe both sisters arranged for this routine the night before.
But yeah, until actually proven otherwise, Kuroiwa's older sister is on my shitlist.