Reina Kuroda holds the position of student council president at Saint Union Academy, characterized by her aubergine-dark hair and brown eyes. She actively resists reviving the school's Circlet Bout club, which closed following the departure of her older sister Ayana Kuroda—a former top player who left for America's advanced training facilities. This exit accelerated the club's decline before Reina enrolled, placing her in direct conflict with protagonist Yuuka Sasaki, who campaigns for the club's return.

External pressure from Takamori Academy's practice match challenge forces Reina to permit the club's revival. Unofficially competing in this match, Reina loses her bout, hindered by a "losing mentality" and wavering confidence, starkly contrasting with Yuuka's surprise victory. Her combat style employs a lance as her Circlet Bout weapon, echoing her sister's techniques but executed with diminished effectiveness.

Reina's refusal to rejoin stems from her conviction that Circlet Bout cannot restore Saint Union's reputation. However, ongoing interactions with Yuuka and club members slowly reshape her perspective, resulting in unofficial participation in club activities. Her evolution involves confronting her sister's legacy and reassessing her own potential role in the team's future.