[Ahemaru] Ushiro kara Netorare [Decensored]

Blackmailed over a video of her kissing her childhood friend Ren, Yuka strikes a filthy deal with her school's lecherous old administrator—her pussy stays faithful to her boyfriend, but her ass is fair game. What begins as reluctant anal servitude escalates into relentless training with giant dildos and speculums, even as she keeps up a smiling, everyday facade beside the oblivious Ren. When summer break arrives, the stakes climax in an anal sex duel broadcast straight to her boyfriend's phone, where victory means freedom and her secret—but losing means Ren sees exactly how far she's been stretched.