[GS-421] My cousin, who had grown into an adult body, came over to my place for a visit and took a bath! While living alone, my cousin, who had grown into an adult body, came over to play and took a bath! I couldn't help but peek and got an erection, and innocently, she said, 'Let's take a bath together for the first time in a long time!' I thought, 'No, I'm already fully erect and...,' but without hesitation, I remained fully erect...