Miri Yōbami belongs to the Yobami family, one of the Hundred Devouring Families under the Momobami clan, renowned for its expertise in pharmaceuticals, medicine, and poison development. She and her older sister, Miyo Inbami, grew up in closely linked families, forging an exceptionally strong bond. When both the Inbami and Yobami families faced a shortage of heirs, Miyo and Miri were designated as their respective clan heads. This role forced their separation, prohibiting direct interaction during family gatherings. To circumvent this, the sisters developed a subtle, non-verbal sign language using gestures and eye contact, which became their primary means of communication throughout their upbringing. Miri possesses a distinctive appearance: short stature, dark blue hair styled in two round "dumpling" buns, and empty dark blue eyes. She typically wears red eye shadow and the standard female uniform of Hyakkaou Private Academy. Her expression remains consistently serious or blank, creating an unapproachable demeanor. Her personality is reserved and distant, rarely speaking beyond terse sentences. She avoids physical affection, defying expectations like refusing Yumeko Jabami's hug. Miri exhibits little sympathy for others' well-being, strategically endangering lives during gambles without hesitation. However, her loyalty to Miyo is absolute, prioritizing her sister's safety above all else. She defers to Miyo's decisions during collaborative gambles, demonstrating unwavering trust. This devotion culminates in self-sacrificial actions, such as deliberately losing critical games to protect Miyo despite emotional distress. During the Hyakkaou Private Academy student council presidential election, Miri arrives with other Hundred Devouring Family members to challenge Kirari Momobami. She initially warns candidate Erimi Mushibami about the risks of seeking power. Alongside Miyo, she defeats Yuriko Nishinotouin by poisoning her, later dismissing Yuriko's fragility. The sisters then face Yumeko Jabami and Ryota Suzui in "Nim Type Zero." Before the game, Miri declares them enemies and avoids formalities. She communicates her cards to Miyo using their sign language during gameplay. In a pivotal moment, Miri introduces a rule requiring losers to self-administer poison via needle. After losing a round, she complies. Forced into high-stakes bets in subsequent rounds, she accumulates unsustainable debt. When Miyo commands her to lose intentionally to ensure Miyo's victory, Miri obeys despite visible emotional pain. This loss eliminates her from the election with a debt exceeding 10,000 votes (the school's total). She collapses from poisoning, but Miyo administers an antidote and hospitalizes her. Miri later recovers, attends the "100 Vote Auction," and reflects on their miscalculation regarding Rei Batsubami's betrayal. Though no longer gambling, she monitors the election and expresses concern for Miyo during the Grand Tournament. Miri's name reflects her background: "Miri" combines the characters for "three" (三) and "reason/logic" (理), while "Yobami" derives from "light/sun" (陽) and "bite" (喰), sharing the "bami" suffix with other clan families.