GG-265 Older sister's real sex education Yui Fujishima

Yui, whose mother has already passed away, lives with her father and younger brother Ma-kun. One day, Ma-kun's girlfriend's friends make fun of him for not knowing anything about sex. When Yui saw this, she decided that she had to teach Ma-kun the correct sexual knowledge as her mother, so she took it upon herself to teach Ma-kun about sex. However, since then, Ma-kun has gotten carried away...