Mihoshi Tachibana is Misato Tachibana's younger sister, introduced in Episode 18 of the anime series. She possesses light aubergine hair with two thin strands extending nearly to her shoulders and matching aubergine eyes. Mihoshi typically dresses in a black-and-white school uniform and carries a long green case on her back housing her shinai for kendo practice.

She maintains a generally positive relationship with her older sister but occasionally teases Misato about her romantic feelings for Koujirou Sasahara. Despite her overall nice demeanor, Mihoshi harbors a temper and, like her sister, may draw weapons when provoked—though less frequently. A notable quirk is her tendency to laugh at others' misfortune or embarrassment, such as when she chuckled at Yuuko Aioi's mishaps on a train while guiding her to a restaurant. Mihoshi struggles to suppress this laughter but often fails.

Passionate about kendo, she trains rigorously even on weekends to improve. Mihoshi feels jealous of Yoshino Naganohara's natural kendo prowess, especially since Yoshino no longer attends practice yet remains seemingly unbeatable. While acknowledging Yoshino's strength, Mihoshi does not fully accept this superiority and sometimes voices critical remarks about her. She is affiliated with friends and classmates Sumika and Tanabo. During one kendo session, Mihoshi accidentally struck the Assistant Instructor while attempting to hit Yoshino.

Her surname, Tachibana, combines the characters for "standing" and "flower/blossom." The given name Mihoshi allows varied kanji interpretations, including "beautiful star," "sea star," or "compassionate star."