Mio Watanabe is a former student at the high school where the main events of the series take place. She served as the president of the club that preceded the tesaguri club, known as the Seishun Mosaku-bu, or Youth Exploration Club. By the time of the main seasons, she has already graduated, but she appears in flashback sequences and as a recurring supporting character in the second season and the spin-off. Her most notable appearance in the spin-off occurs in episodes five and twelve. Mio has a somewhat rough or intimidating appearance that leads the other characters to frequently mistake her for a delinquent. However, she strongly denies this characterization, arguing that a genuine delinquent would not bother participating in club activities. Despite her tough exterior, she admits to having a fear of pointed or sharp objects. Her personality is often the target of teasing from the main cast, who enjoy provoking her exasperated reactions. As the former club president, Mio was responsible for leading the brainstorming sessions that defined the club, and she takes pride in having laid the foundation for the tesaguri club's creative, improvisational spirit. Her key relationship within the series is with Aoi Takahashi, who was recruited into the club during Mio's tenure as president; this connection is explored in an episode that details the year Aoi joined. She also knows Yua Suzuki and Hina Sato as underclassmen from her time leading the club. Mio's role in the story is primarily to provide historical context for the club, bridging the gap between its earlier days and the current generation. While she does not undergo significant personal development due to her limited screen time, her appearances help reinforce the club's legacy and the continuity of its members. Her notable abilities lie in her experience with improvisational club activities and her quick thinking during discussions, while her unique fear of pointed objects often serves as a humorous character trait.