Minazuki Rokumatsuri, called Mina, is the adopted younger sister of series protagonist Chitose Hitotose. Her surname reflects the number six, and her given name, Minazuki, traditionally signifies the sixth month. She shares an orphanage childhood with Chitose and her biological older sister, Hazuki Yazakura. Following adoption, Minazuki and Hazuki were separated from Chitose until reuniting after he moved into his parents' former home. Minazuki now attends middle school on the same campus as Chitose and resides in a nearby apartment with Hazuki, though Hazuki's frequent pop idol tours often leave her alone.

Minazuki maintains a close, supportive relationship with Chitose, displaying deep familial affection while simultaneously harboring longstanding romantic feelings for him. She openly declares her intention to marry him when she is old enough, an aspiration consistently present throughout her story. In the sequel *Happy Lesson Advance*, Minazuki continues her studies and navigates her relationship with Chitose. Her romantic intentions persist unchanged even as new dynamics emerge, such as the sibling-like rivalries introduced by Nagatsuki Kuron's arrival based on her claim to be Mutsuki Ichimonji's rightful child.

Visually, Minazuki is depicted as a teenage girl with distinctive pink hair reaching her chest and matching pink eyes. Her design remains consistent across all media adaptations, including the original manga, OVAs, television series, and video games. Her characterization consistently emphasizes her supportive nature towards Chitose alongside her steadfast romantic goal, which remains unresolved.