Ever since being insulted by his cheeky stepsister upon their very first meeting, our protagonist has only been able to get off to little-sister stories aimed at hardcore masochists. One day, while he’s masturbating as usual, recalling her harsh words, the very girl herself catches him in the act! Backed into a corner as she threatens to tell their parents, he’s suddenly tempted when she says, “I’ll let you fuck me for 100,000 yen”…!?