Rumi acts as a vice-commander alongside two others under Alice Shimada in the All-Stars University Team, leading the 'B' Squadron. She pilots an American M26 Pershing tank displaying a blue triangle on the front during official matches, utilizing an M4 Sherman for training observations. Short in stature, she has greyish-purple hair, blue eyes, and consistently wears glasses along with the All-Stars University Team's Sensha-dō uniform and hat. Her personality includes being a "Hard-Drinking Party Girl" with poor cooking skills, traits shared with teammates Azumi and Megumi, forming the "Bermuda Trio". She holds strong admiration for Alice Shimada's cuteness. Background details from Drama CDs reveal she previously attended Jatkosota High School before university, where she knew Mika, Mikko, and Aki, whom she considered Jatkosota's "weirdest" students. During the film's events, Rumi first appears with Azumi and Megumi observing Alice Shimada's training in M4 Shermans. Commanding a company of seven M26 Pershings and one M24 Chaffee in the match against Ooarai, she engages Team Dandelion in a long-range gunfight across wetlands to pin them down. Her forces withdraw after Ooarai destroys the Karl-Gerät artillery. Later, she pursues the Panzer IV and Hetzer through a maze with two Pershings and a Chaffee. After losing the Pershings, she spots the CV.33 acting as a spotter on a rollercoaster and dispatches two Chaffees to intercept it. She then reunites with Azumi and Megumi as the "Bermuda Trio", eliminating several Saunders tanks before her Pershing is rammed by a T-34/85 and knocked out by a Tiger II. Her additional appearances include spectating matches between Continuation High School and Saunders, and later between Continuation and Oarai, in *Das Finale 3*. A notable point is her status as the only Bermuda Trio member failing to regroup with Alice Shimada in Central Plaza because her tank was immobilized by Erika Itsumi. Her name follows the pattern shared with the other vice-commanders, ending with "ミ" ("-mi").