Chōhi Yokutoku, known privately as Rinrin, endured the tragic loss of her parents to bandits early on. Raised afterward by her grandfather, his eventual death left her profoundly alone. To combat this loneliness, she formed the "Rinrin Bandits" with village children, pulling disruptive pranks. This led local officials to attempt her arrest, prompting Kan'u to intervene and confront her personally. After a lengthy battle, Kan'u challenged Rinrin's actions, causing Rinrin to break down emotionally, confessing her deep loneliness and lack of purpose. They spent the night together, forging a vow of sisterhood; Rinrin affectionately calls Kan'u "onee-chan." This marked the start of her journey with Kan'u to fight injustice across China.

Rinrin displays a cheerful, energetic, and tomboyish personality, often speaking in the third person and using the verbal tic "nano-da." Beneath her exuberant exterior lies deep fragility from her traumatic past, manifesting as a fear of abandonment and occasional emotional vulnerability, like breaking down on her birthday after dreaming of her deceased parents. She is fiercely loyal and dedicated, defending villages against bandits even while severely ill. Her naivety shows in her lack of understanding about romance and sexuality, leading to unintentionally comedic situations such as misnaming military operations with double entendres. She is prone to jealousy when Kan'u forms close bonds with others, initially opposing Ryūbi's inclusion into their sisterly dynamic.

Physically diminutive, Rinrin possesses exceptional combat prowess, specializing in powerful slashing spearmanship rather than thrusting techniques. Her strength lets her effortlessly wield a massive spear, send multiple enemies flying with single strikes, and lift heavy objects like battering rams single-handedly. She demonstrates enhanced agility, reflexes, and stamina, enabling her to match Kan'u in battle. Her background as leader of the Rinrin Bandits honed skills in trap design and guerrilla tactics, which she employs strategically. However, she lacks technical finesse, making her predictable to skilled fighters. Additional weaknesses include low intelligence, illiteracy, impatience, and susceptibility to illnesses like the common cold, which significantly impairs her.

Her relationship with Kan'u is central, characterized by intense devotion and a "big sister complex." Rinrin frequently seeks physical affection, such as resting in Kan'u's lap, and becomes jealous when others vie for Kan'u's attention. She openly brags about their sisterhood vow, often recounting their initial night together in ways that cause misunderstandings. In the visual novel continuity, she forms a similar bond with Kazuto (the protagonist), treating him as an older brother and calling him "onii-chan." Her romantic feelings for him evolve from familial affection to conscious attraction, leading her to seek advice on enhancing her femininity. In later anime seasons, she reluctantly accepts Ryūbi as another sworn sister after Ryūbi becomes Kan'u's older sibling, eventually referring to Ryūbi as "Tōka-neechan."

Her character development varies across media. In the visual novel, she transitions from obliviousness about romance to actively pursuing Kazuto, consulting others on womanhood and wearing dresses to appeal to him. The anime emphasizes her unwavering loyalty and combat dedication, like single-handedly protecting villages while ill. Her acceptance of Ryūbi as a sister in the third season illustrates growth in overcoming jealousy. Spin-offs and OVAs highlight recurring traits, like her trap-setting skills reused for comedic effect and her inclusion in idol groups. Distinctive elements include her tiger-themed hairpin that changes expressions with her moods, her habit of going barefoot, her large appetite, and comedic misadventures with wildlife she mistakes for childhood pets.