KASE-SAN!!!
When your adorable girlfriend who has a heart of gold and is as pure as a child wants to buy kigurumi pajamas for both of you to wear in a pair-look style, you indulge her! You do NOT try to dress her in sexy see-thru lingerie!
It is an amusing truth that Kase is, in fact, the more adult of the two. Yes, even after betting on a race her moving out of the dorm. (As people have explained before, in Japan putting your workplace and workmates -- or in this case studyplace and studymates -- before your significant other is considered a sign of maturity and responsibility.)
For Yamada, conjugal bliss means dress in cute teddy bear pajamas, have dinner together, talk about how your day went, watch tv, maybe cuddle and kiss if the mood is right. For Kase it's more like sex, sex, sex. Getting Yamada to wear erotic lingerie? Even better.
Go to horny jail, you wretch.
If lusting after Yamada is reason enough to be sent there, she should think about making it her permanent residence.