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At the age of 30, Taro, who has become concerned about the fat around his stomach, has been able to train his body as a personal trainer by Ayuka, who is also a sister-in-law, at the recommendation of his brother. Then, on the first day, Taro's crotch swells out of his tight training wear as he stretches his body with Ayuka. Ayuka doesn't even look at Taro's crotch... A few days later, the two are sweating and training again. His sister-in-law's coaching brings changes to Taro's body, but...