Tsubomi Okuwaka is a first-year student at St. Spica's Girls' Institute on Astraea Hill, recognizable by her waist-length taupe hair held back by a black headband and her yellow eyes. She wears the standard St. Spica's uniform, the choir uniform, and yellow-themed sleepwear with brown and orange accents.

Despite her age, Tsubomi often acts mature and commands attention with her forceful, outspoken personality, even intimidating senior students. She readily lectures peers like Hikari Konohana and Yaya Nanto about academics and conduct, though she herself is easily flustered or angered, especially when embarrassed by interactions involving Hikari or comments from others.

Tsubomi initially harbors strong admiration for Hikari Konohana, frequently denying it as a crush despite clear evidence. She joined the St. Spica Choir because of Hikari, a motivation she dismisses with embarrassment. Interactions with Hikari provoke visible shyness: avoiding eye contact after receiving gratitude, becoming overwhelmed seeing Hikari in an apron, or blushing when others anticipate Hikari's grace. Tsubomi openly criticizes Spica's room temp system, declaring she would only serve someone she chooses—implicitly Hikari.

Her focus later shifts toward Yaya Nanto. During the Etoile election, Tsubomi notices Yaya's sorrow over Hikari's participation and sympathetically stays by her side. She invites Yaya to a night tea party while denying concern as the reason, and chooses to remain with Yaya instead of watching Hikari's event, self-deprecatingly calling herself "an idiot" for this choice. Tsubomi grows shy and nervous around Yaya, particularly during playful teasing, and their interactions imply a budding romantic relationship, including indications they start dating.

Tsubomi performs as Juliet opposite Kagome Byakudan's Romeo in the school's cultural festival adaptation of *Romeo and Juliet*. Light novels and manga depict her serving as secretary for Spica's student council, a role omitted in the anime adaptation.