Mikawa is Yui Yamada's high school best friend, affectionately nicknamed "Mikawacchi" by Yamada. She displays a protective streak upon learning of Yamada's relationship with Tomoka Kase, fueled by rumors about Kase's dating history. Mikawa's sharing of these unverified rumors amplifies Yamada's insecurities, though they are later disproven—Kase had no prior romantic partners during her track club days.

Boisterous and energetic by nature, Mikawa harbors a distinct aversion to blood, reacting intensely to incidents like Yamada's injuries. Despite initial reservations about Kase, she becomes supportive of their relationship after the rumors dissolve, remaining Yamada's trusted confidante as she navigates feelings for Kase.

After graduation, Mikawa relocates to Tokyo for college, pursuing tourism studies. This places her in the same city as Yamada and Kase, who move there for horticulture and sports studies respectively. She sustains her friendship with Yamada through their college years.

In the sequel series centered on Yamada and Kase's college life, Mikawa continues as Yamada's friend while attending Tokyo college alongside the main characters.