Chōhi Yokutoku, known as Rin Rin, endured significant personal tragedy when bandits killed her parents during her childhood. Raised by her grandfather, his death later plunged her into profound loneliness. This isolation drove her to form the "Rinrin Bandits" with other village children, a group specializing in pranks against villagers. The escalating situation led the village chief to authorize her arrest. Kan'u intervened, offering to apprehend Chōhi herself. During their confrontation, Kan'u challenged Chōhi about inflicting suffering on others despite her own past trauma, prompting Chōhi to break down and confess her deep isolation. Kan'u spent the night with her, and they pledged a vow of sisterhood—an event Chōhi later described as being "pledged in bed," phrasing that causes recurring misunderstandings.

Chōhi exhibits a cheerful, talkative, and tomboyish personality, often masking underlying emotional fragility. She consistently speaks in third person and uses the verbal tic "nano-da". Her attachment to Kan'u is intense, reflecting a "big sister complex"; she initially opposed Ryūbi becoming Kan'u's younger sister in the second season, though she later accepted Ryūbi as an additional older sister, referring to her as "Tōka-neechan". She demonstrates fierce loyalty to allies and dedication to duty, exemplified by defending a village against bandits while severely ill. Naivety defines her understanding of romance and sexuality, leading to unintentional comedic situations—such as coining the term "Operation Houkei-Peeling" unaware of its dual meaning.

Physically, Chōhi possesses exceptional strength disproportionate to her small stature, enabling her to wield a massive spear with ease and match Kan'u in combat. Her combat style favors powerful slashing motions over thrusting, leveraging the spear’s forked blade. She displays enhanced agility, speed, and stamina. Her leadership experience with the Rinrin Bandits translates directly to tactical proficiency in trap design and battlefield command. Weaknesses include a reliance on raw power over technique, impatience, low intelligence, illiteracy, and vulnerability to illness—a cold significantly impaired her abilities.

Her character development involves confronting deep-seated trauma, such as an emotional breakdown on her birthday after dreaming of her deceased parents, which led Kazuto to vow to alleviate her loneliness. Romantic feelings for Kazuto evolved from sibling-like affection to genuine attraction, driving her to seek advice on womanhood and occasionally wear dresses to appear more feminine. Across the series, her relationships expanded to include Ryūbi as a sisterly figure, though her central bond with Kan'u remained, often expressed through physical affection like lap-sitting or embracing.

Distinctive traits include a tiger-shaped hairpin that changes expression with her mood, her habit of going barefoot, and associations with animals—such as mistakenly identifying wild bears or boars as childhood pets. She is also noted for her exceptionally large appetite, grouping her with characters like Bachou and Ryofu.