After being flagged for abnormalities during a company health checkup, Sato begins morning jogs before work with his supervisor, Mr. Oshima, and his wife. However, the athletic wear borrowed from Mr. Oshima is extremely tight, causing his sensitive nipples to chafe repeatedly, forcing Sato to quit exercising early. When Yuka Oshima notices his reaction, she finds it amusing and starts deliberately tormenting his nipples under the guise of treatment. Sato writhes and cries out, and his responses awaken Yuka's sadistic side—fueled by her own pent-up desires—plunging her deeper into the thrill of dominating him. Over time, repeated nipple torture becomes routine, and as she grows increasingly fascinated by his reactions, their twisted relationship intensifies.