Hazuki Yazakura is one of the primary characters in the Happy Lesson franchise, introduced in the original OVA series. She is the older adopted sister of the protagonist, Chitose Hitotose. Hazuki, along with Chitose and their younger sister Minazuki Rokumatsuri, comes from the same orphanage or children's facility, and they formed a familial bond there before being taken in by their guardians at the series' start. Unlike Chitose, who lives with his five teachers, Hazuki shares an apartment with Minazuki not far from Chitose's house.

In terms of appearance, Hazuki is depicted as a tall, glamorous young woman with long, straight hair. Her physique is notably mature and well-proportioned. Her personality is cheerful and easygoing; she does not tend to worry about trivial matters and approaches life with a positive, energetic demeanor. One of her most defining and humorous traits is her voracious appetite. She is portrayed as a legendary master of the "Great Eating Path," a title that humorously acknowledges her ability to consume vast quantities of food, particularly sweets. Despite her glamorous public image, her down-to-earth and enthusiastic love for eating adds a layer of relatable charm to her character.

Hazuki's primary motivation and role in the story stem from her deep affection for her adopted family. She loves Chitose and Minazuki as if they were her own younger siblings, displaying strong protective instincts and a desire to care for them. This maternal love is evident in her interactions, and she holds great trust in the group of five teachers, known as the Mama Sensei, who act as Chitose's surrogate mothers. Early in the series, her attachment to Chitose leads to a rivalry with the five teachers. Upon hearing that Chitose lives with his female teachers, she misunderstands the situation and initiates a series of competitions to win the right to live with and take care of him herself.

Regarding her career and abilities, Hazuki is a successful professional rock singer or pop star who performs concerts in various locations. Her career as a performer is a significant part of her identity and explains her busy schedule, as she travels frequently for tours. Her primary "ability," aside from her musical talent, is her legendary capacity for eating, which is a recurring source of humor and a defining character trait. As a rock singer, she is also considered a celebrity, adding a layer of public attention to her private life.

In terms of character development, Hazuki achieves a major goal related to her martial arts mastery early in the first season, after which her activity level temporarily decreases before she regains her usual energetic spirit. Her role in the narrative expands in later seasons, where she is described not just as a popular singer but as a legendary, world-famous artist. Throughout the series, she serves as a bridge between Chitose's chaotic home life with his teachers and his past at the orphanage, providing a sense of familial continuity and unconditional support for her younger siblings.