A married woman named Miyu, who was told by her loving husband, "Have you gained a little weight?", decided to go on a diet. She wanted to lose weight healthily by sweating it out at the gym under the trainer's guidance. However, the trainer keeps touching her insistently. Before she knows it, she's exposed to her breasts, and the trainer starts teasing her with his cock right in front of her. But as Miyu looks at the trainer's cock, she starts to feel a strange sensation. As if sensing her feelings, the trainer takes off her pants and inserts his hard-on cock into her from behind. Despite her confusion, Miyu can't help but moan with pleasure. Once this happens, there's no stopping! Miyu, intoxicated by the guilt of betraying her husband, dives headfirst into an adulterous affair.
