Big Sister's Real-Life Flexible Education: Kimura Tsuna GVG-413

Kimura Tsuna lived happily with her family, but her younger brother was hospitalized. One day, she went to visit him to cheer him up. At that moment, her brother's pubic hair was being shaved for surgery, and his penis became fully erect. So, under the guise of sex education, she used her brother as a practice subject for sex...