Mikuni Katō attends Itan Private High School, progressing from Class 1-1 to Class 2-2 and finally Class 3-4. Her brown hair is typically styled in circular braids, and she wears distinctive circular glasses. Hailing from a wealthy family, she resides in a spacious traditional Japanese mansion and often wears a kimono at home. Her mother is Yakuna, and her grandfather, a former professional shogi player, taught her the game and continues to support her practice. She first encounters Komi Shouko and Ayami Sasaki during Komi's first-year field trip, grouped by lottery. Katou crafts a detailed itinerary to ensure Komi enjoys the trip, though she initially clashes with Sasaki over scheduling. Komi helps reconcile them, forging a strong friendship among the trio. This experience shifts Katou's view of Komi from unapproachable to relatable. Katou and Sasaki develop a close bond, regularly hosting "girl talk" sessions at Katou's mansion. They discuss romantic topics, especially Komi's relationship with Hitohito Tadano, which Katou analyzes using shogi-like strategy. Her intuitive insights aid Komi's social growth and strengthen their friendships. Katou aspires to become a professional shogi player capable of competing equally with male professionals. She reached the Women's Phoenix Shogi Tournament semifinals and often channels thoughts of romance into competitive focus. During a critical match at the Shogi Hall, a telegram from Sasaki about Komi and Tadano's relationship progress reignites her momentum, leading to a comeback victory. She later assists Tadano and Komi with shogi strategies, facilitating their interactions. She feels romantic interest in Makoto Katai, drawn to his intense eyes. This attraction frequently surfaces in talks with Komi and Sasaki, often prompting Katou to react with light shoulder punches when teased. Her friends note similarities between Katai and a character from her favorite manga, "From Today, This Is!!". Academically, she ranked 16th out of 150 students in her second-year summer finals. She served as class president during her second year, maintaining friendships with Komi, Sasaki, Kiyoshi Isagi, and others. Trivia notes her preference for strawberry daifuku, her name's reference to shogi player Katou Hifumi, and her 21st-place ranking in a series popularity poll.