Minazuki Rokumatsuri is the adopted younger sister of Chitose Hitotose and one of the heroines in the anime Happy Lesson. She and Chitose grew up together in the same orphanage, and she currently attends the middle school section of the same campus where he is a student. She lives with her older sister Hazuki in an apartment building not far from Chitose’s house, though Hazuki is often away on tour. Her birthday is June 6, she has red hair and red eyes, stands about 1.45 meters tall, and has blood type O.

Mina, as she is often called, is a cheerful, affectionate, and somewhat naive girl. She deeply loves Chitose as a brother figure and is always eager to help him in any way she can. Her feelings for him go beyond sibling affection: she openly declares her intention to marry him when she is old enough, though she does not push the issue aggressively and generally respects the boundaries of their relationship. Her primary motivation is to stay close to Chitose and to support him, and she takes her role as a younger sister seriously.

In the story, Mina serves as a recurring supporting character and one of the several young women in Chitose’s life. She adds a youthful, innocent perspective to the household dynamic and often provides lighthearted comedic moments through her earnest crush. Her relationship with Chitose is central to her role; she also shares a close bond with her sister Hazuki, and she interacts with the other female teachers and students who live with or around Chitose. Over the course of the series, Mina remains a consistently devoted and caring presence, showing subtle signs of growing older and more mature but never losing her core affection for her adopted brother. She has no supernatural or extraordinary abilities; her notable trait is her unwavering loyalty and her determination to be a good sister and student.