[Nanonan no Tei (Nanonanno)] JK Kuppuku Kousoku ~Aikidou Shoujo ga Maketa Hi~

A proud aikido-trained schoolgirl learns the cost of losing when blackmailers dangle Haru-kun's safety over her and she whispers that she'll do it. Cornered against a tree, then bound in cuffs and chains, she is fingered and used until her disciplined body betrays her, trembling through every squelching command to hurry up and fall. By the final spread she lies strapped and twitching, spiral-eyed and gasping that she can't breathe as rough treatment pushes the girl who never loses past the point of no return.