Iroha Miyamoto is a fifteen-year-old martial artist representing the Miyamoto clan, embodying the Snake among the twelve Chinese zodiac families. Her family's formidable past as a feared yakuza group crumbled under her father's kind-hearted leadership, his nature unable to retain hardened members. This decline leaves Iroha and her loyal subordinate, Hanzō, as the clan's sole remnants.

Initially, Iroha targets Kōshi Inuzuka for assassination to halt his marriage to Momoko Kuzuryū. She aims to reignite warfare among the zodiac families and restore her clan's dread reputation, aligning herself with western families opposing the union. Momoko's protection of Kōshi thwarts this attempt. During the conflict, unexpected feelings for Kōshi surface within Iroha, compelling her to renounce her lethal mission.

Shifting her path, Iroha enrolls in Kōshi's school to be near him. Her evolution transforms her from a mysterious, reserved fighter into a more expressive teenager, openly displaying emotions like jealousy and forging friendships. Momoko Kuzuryū's recognition of Iroha's strength, coupled with lamenting her assassin path, catalyzes Iroha's search for a new, non-violent purpose for the Miyamoto clan.

Petite in stature, Iroha possesses long blonde hair often secured in a side ponytail and brown eyes. Her signature attire includes a short purple yukata with a light brown obi, black elbow warmers, fishnet stockings, black shin guards, sandals, and a chain necklace. She typically carries a sword, exchanging it for school attire when required. Her surname "Miyamoto" (宮本) incorporates characters signifying "snake," "house/dealer," and "base/origin," mirroring her clan's identity.

Her bond with Hanzō is rooted in unwavering loyalty; he remained by her side after she saved his life when others abandoned the clan. She regards him strictly as family, rejecting any romantic possibility. As events unfold, Iroha supports Momoko's pursuit of Kōshi's affection despite her own burgeoning feelings.