Tei, designated as a Taiwanese T91 assault rifle, serves as treasurer of Seishou Academy's student council. Her most distinctive feature is her hairstyle: six pigtails. This leads Ichiroku (M16A4) to nickname her "Fountain" or "Fountainhead" due to the resemblance to water spraying from a fountain.

Her attire includes a G-string featuring an adjustable waistband, directly referencing the collapsible telescopic stock of the real T91 rifle and allowing similar functional adjustments. In personality, she is supportive and level-headed, particularly towards her close friend Aug (Steyr AUG). Tei actively assists Aug in managing her dual personalities—timid short-haired and aggressive long-haired—especially during Aug's attempts to confess romantic feelings toward Funco (FNC). She intervenes to mitigate Aug's embarrassment or emotional outbursts, ensuring interactions remain calm.

Tei enjoys cooking and considers Aug's food preferences when preparing snacks. She occasionally exhibits a verbal tic, ending statements with "~ne," which may reflect linguistic mannerisms associated with her Taiwanese origin within the series.

During the jungle wargames tournament arc, Tei participates alongside Aug in a battle against Ichiroku. Ichiroku shoots off Tei's adjustable stock, damaging it and highlighting the anthropomorphic link between the characters and their respective firearms. Her role remains consistent as a secondary character focused on supporting Aug and fulfilling student council duties.