Tasked with caring for her brother, Milky-chan discovers his hidden desires and decides to secure her place in his life by becoming his sexual guide. Using a sex manual as a guide, she transforms their relationship into a series of provocative "lessons," indulging his fetishes and boundaries to ensure she is the only woman he ever needs.
After discovering her brother's interest in erotic literature, Milky-chan decides to take his sexual education into her own hands to ensure she remains the only woman in his life. She guides him through a series of intimate "lessons" that escalate from simple touch to full intercourse, cementing their taboo relationship.
Milky-chan takes charge of her brother's care and decides to use a sex manual to "educate" him on the female body, hoping to secure her place as his girlfriend. As she guides him through various fetishes and intimate acts, she finds herself unexpectedly overwhelmed by her own arousal and the intensity of their forbidden connection.