Komachi Mikumari is a young girl from the farming village of Kanna. She is the younger sister of the village's water priestess, Kirara. Demonstrating a precocious and determined nature from the start, Komachi insists on joining her sister and the villager Rikichi on their journey to the city to recruit samurai to defend their home from the predatory Nobuseri bandits. She is physically small, with short brown hair, pale skin, and brown eyes, and she wears a blue villager uniform.

Her personality is a bundle of boundless energy and insatiable curiosity. She is exceptionally blunt for a child, possessing a charming lack of filter that leads her to ask questions others might avoid. This directness, along with her constant activity and spirited disposition, makes her an immediate and memorable presence. She is brave for her age, never succumbing to tears or requesting to go home despite the dangerous situations the group encounters, and she rarely complains about hardships.

Komachi's main motivation is her thirst for adventure and her desire to support her sister. She sees the journey as a great opportunity to explore the world beyond her village. As a future Water Maiden, she is being groomed to eventually take over Kirara’s spiritual duties.

Her closest relationship is with her sister, Kirara. Among the gathered samurai, her favorite is the boisterous cyborg Kikuchiyo, whom she affectionately calls Kiku. She is often seen riding on his shoulders, and she playfully asks him to marry her when she grows up, a request he wryly indulges, seeing her as a daughter-like figure and playmate. She also forms a friendly, little-sister-like bond with the young samurai Katsushiro, whom she calls Katsu. Remaining connected to her home, she constantly writes letters to her best friend Okara, keeping her informed of the group's adventures.

Over the course of the story, Komachi does not undergo a dramatic personality shift but instead steadily reaffirms her inner strength and loyalty. She consistently brightens the mood of the group and provides an innocent, childlike lens through which the harsh realities of the conflict are viewed. Her greatest development is revealed at the story's conclusion, where after the final battle against Ukyo, she formally takes on the mantle of the new water priestess for her village. This signifies her transition from a curious, energetic child into a responsible and vital guardian of Kanna’s future and traditions.