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 friends make fun of him for not knowing anything about sex. Seeing this, Yui decides to teach Ma-kun about sex on her own, saying that she has to teach Ma-kun the correct sexual knowledge for her mother. However, since then, Ma-kun has gotten carried away...