Iina Chiyo, formally known as Iinchou, holds the class presidency at Isono Junior High School. Her presence remains passive and frequently overlooked by classmates, who consistently address her by her title instead of her personal name. She shares a close bond with Mawari Zenigata. Physically, she possesses green hair and eyes, wears glasses, and has a well-endowed figure; removing her glasses noticeably enhances her appearance, occasionally causing reactions like Nagasumi Michishio's blushing.

Secretly harboring deep unrequited affection for Nagasumi, she attempts to confess via a love letter but mistakenly addresses it to Seto San after failing to look directly at the recipient. This error triggers her transformation into an alternate persona—the "Last Amazoness," a confident, girl-loving warrior who aggressively pursues San. Iinchou adopts this persona to gain attention or bolster her confidence during challenges. Later, she collaborates with Maki, whom she perceives as a fairy, and obtains the gender-reversing mermaid weapon "Gender-X" from Surtan. As the Last Amazoness, she actively combats troublemakers using this weapon. A recurring personal goal involves her desire for others to discover her real name, which remains unrealized until the manga's conclusion. Mawari Zenigata finally reveals it as "Iina Chiyo," prompting her triumphant reaction.