I’m not an NTR fan and I honestly can’t wrap my head around how NTR fans think. Still, Japanese eroge are packed with NTR subject matter, for better or worse. NTR here doesn’t mean what grade-schoolers mean by “the girl you like doesn’t like you, she likes someone else.” It’s 寝取る — and the meaning is simple: your wife, your spouse, your lover, your girlfriend got slept with by someone else. Put plainly, you got cuckolded. Even if you’ve spent years lurking Reddit, ACFUN, the greening street, and the Thunder Bluff of 5ch, I’ve never once seen a guy discover he’s been cuckolded and feel happy about it. So yeah, the NTR fan mindset is hard to get. And yet NTR games keep coming out. Plenty of companies make them, some even set up a dedicated brand just for NTR titles to chase that specialist credibility. Like this one, Houkago ni Midareru Ane Kyoushi to Tonari no Heya de Aegu Imouto (放課後に乱れる姉教師と隣の部屋で喘ぐ妹 ～恋人になった女の子が、知り合いの嫌な男に寝取られる～), which bills itself as a standard NTR game.