A collaboration project between SODSTAR and Momoiro Kazoku. A college-aged sister secretly likes her younger brother. Mahiro makes up her mind and gets in the bath completely naked while her brother is taking a bath. It's the first time they've had a bath together in 10 years. Her brother is surprised, but his penis gradually grows and they cross the line. From then on, the two of them seek each other's bodies many times, and they start having forbidden creampies without a condom...