Miwa Mikadono is the youngest of the three Mikadono sisters and a central protagonist in the story. She is a first-year student in the advanced track at Saika Academy, the same prestigious institution where the sisters are collectively known as the Three Royals or Three Emperors due to their exceptional talents. Miwa is recognized as a prodigy in shogi, a game at which she is considered unbeatable, and she also excels in other strategic disciplines such as chess and mathematics. Her background reveals that her passion for shogi did not arise naturally; instead, she was pressured by her father from childhood to achieve visible results, and she chose shogi as an outlet best suited to her analytical gifts.

Personality-wise, Miwa presents a contrast between intellectual maturity and childlike tendencies. She is highly intelligent, analytical, and tends to view the world through strategy and logic, often speaking in a distinctive manner, using the first-person pronoun uchi and ending her sentences with ssu. She exhibits a clever wit and a slightly mischievous streak, but she is also the most socially awkward of the sisters and can be blunt or detached. Underneath her analytical exterior, Miwa craves attention, especially from Yuu Ayase, and displays a childlike need for care and affirmation. She originally appears emotionally distant from her sisters, but it is later revealed that this distance stems from a deep desire for them to reunite as a close family.

Miwa's primary motivation is rooted in her wish to rebuild the family bond that was lost as each sister became consumed by her own field. Her role in the story evolves as she moves from viewing Yuu as an illogical and inconvenient variable in the household to seeing him as someone who defies her rational predictions. She becomes deeply attached to the stability and warmth he provides, particularly through his cooking and his genuine efforts to support her. Her significant relationships include her sisters, Kazuki and Niko, whom she initially keeps at arm's length, and Yuu, whose presence sparks a deep curiosity and affection in her that logic cannot explain.

Throughout the narrative, Miwa undergoes meaningful development. She learns to move beyond pure calculation and begins to understand human emotions and the value of family. Her growth involves accepting that not everything in life can be strategized and that Yuu's role in her life provides a kind of personal fulfillment no shogi victory can offer. In terms of notable abilities, Miwa is an extraordinary shogi player whose strategic mind extends to other academic and board-game domains. She is also known for her messy hair, a big appetite for sweets, and a mischievous attitude that sometimes comes across as prickly. Her cleverness, combined with her emotional vulnerability, makes her a character who gradually opens up to the idea that even a prodigy needs someone to rely on.