Koharu Senjuin leads her high school's Mountaineering Club as president. She enthusiastically recruits Aoi Yukimura, detailing the club's focus on competitive mountaineering and striving for victory in various competitions. Though eager to welcome Aoi, Koharu fully respects her preference for enjoying climbs at her own pace rather than joining the club's structured activities.

Koharu possesses practical knowledge of mountaineering equipment. Learning of Aoi's planned return attempt to summit Mount Fuji, she advises her to acquire a new backpack engineered to minimize strain and optimize weight distribution during the grueling ascent. This recommendation sends Aoi, accompanied by friends Hinata, Kasumi, Yuri, and Mio, to an outdoor goods store to find suitable gear. Koharu's counsel highlights her grasp of how proper equipment enhances both the climbing experience and safety.

Her role facilitates the main characters' development through club-related opportunities and practical support, operating primarily within the school club structure and specific gear guidance contexts.