A physical relationship between a bloody brother and his sister. My brother and sister, who were close to each other when I was a child, took a bath together and started by singing their younger sister's genitals out of mischief. I gave my parents a reason in the background, and for the first time two people went on a hot spring trip one night and two days. Nakade Sanmai is a pure younger sister who responds to the demands of her brother, who is embarrassed but impure.