Miri Yobami arrives at Hyakkaou Private Academy as a member of the Hundred Devouring Families, part of the Momobami clan, with a clear mission: to remove Kirari Momobami as Student Council President and install new clan leadership. Her family, alongside Miyo Inbami's, operates the clan's medicine business, including poisons, a specialization that ignited historical conflicts within the Momobami branches. She stands petite with dark blue hair tied into two odango buns. Her dark blue eyes appear empty, accentuated by distinctive red eyeshadow at the corners, matching Miyo's. She wears the standard female Hyakkaou uniform. Miri maintains a reserved and distant demeanor, rarely showing open affection and projecting seriousness, especially during gambling. She demonstrates minimal concern for others' lives or well-being, readily endangering them in high-stakes games if it advances her goals. However, her profound loyalty and care for Miyo Inbami override all else; she prioritizes Miyo's life above her own. This deep bond stems from their shared childhood. After their families separated them and forbade direct conversation upon naming them clan heads, they developed an intricate, non-verbal sign language for covert communication. This system allows them full private conversations, frequently used to coordinate gambling strategies. Though Miri typically maintains a cold exterior even towards Miyo, this relationship is her primary emotional anchor. In the presidential election arc, she partners with Miyo. They defeat Yuriko Nishinotouin by poisoning her to win a gamble. Miri later warns candidate Erimi Mushibami that reaching the top makes one a target. She and Miyo then face Yumeko Jabami and Ryota Suzui in Nim Type Zero. Before the game, Miri declares them enemies and discards formalities. During the gamble, she uses their sign language to relay her card information to Miyo. The stakes escalate when Miyo proposes losers inject themselves with a poisoned needle. Miri loses one round and injects herself. Later, weakened by the poison and facing serve chip losses preventing recovery from another defeat, Miri confronts a choice: her own survival or ensuring Miyo's continued participation in the election. Commanded by Miyo, she deliberately loses the game. This sacrifice eliminates her from the race and causes her to collapse unconscious. Miyo administers a second needle dose before rushing her to the hospital. After recovering, Miri attends the auction event but refrains from gambling. She observes the ongoing election, expressing visible concern during Miyo's gamble against Mary Saotome in the Grand Tournament. She also reflects on the collective failure to anticipate Rei Batsubami's betrayal. Her focus remains fixed on Miyo's activities and safety following their defeat.