Ayumi Saitō is a notable character within the story, a sixteen-year-old professional shogi player whose circumstances and choices place him in a unique and challenging position. Physically, he is described as androgynous, a trait that becomes central to his initial method of competing. His background is marked by family hardship; due to his mother's chronic illness, he was forced to leave high school in order to care for her and manage the mounting medical bills. Facing significant financial pressure and the reality that the male professional league would take two years to qualify for, Ayumi makes the pragmatic decision to disguise himself as a girl to compete in women's shogi tournaments, where he could earn prize money more quickly to support his mother.

Ayumi's personality is defined by a fierce determination and a deep, earnest intensity, particularly when it comes to the game of shogi. This drive is fueled by his desperate need to win for his family's survival, making his approach to the board relentless and powerful. Despite the seriousness of his situation, he forms a significant bond with the protagonist, Shion Yasuoka. He first appears as a rival, engaging in a tense and memorable match against her that showcases his formidable will to win. However, their connection runs much deeper. Six months prior to the events of the main story, Ayumi, while in disguise, saved Shion from a stalker, an act for which she later expresses her gratitude. This secret knowledge creates a unique and trusting friendship between them; Shion recognizes him despite his disguise and chooses to keep his identity confidential, while Ayumi becomes a protective and caring figure in her life.

Ayumi’s role in the story is multifaceted, serving as both a friendly rival to Shion and a key supporting character in her emotional journey. Their relationship evolves into a close, trusting friendship where they are each other's confidants. However, his personal life remains fraught with difficulty, primarily due to his abusive father. His father not only emotionally torments him, going so far as to blame Ayumi for his mother's poor health, but also steals the prize money Ayumi earns from shogi matches, claiming it as compensation for having taught him the game. This toxic home environment creates a stark contrast to the support Shion receives from her adoptive family.

Throughout the narrative, Ayumi undergoes significant development. The loss of his mother marks a turning point, after which he abandons his female disguise and chooses to compete openly as a male shogi player. This change is symbolized by an important haircut, representing his decision to forge a new, authentic path for himself in the professional world. His journey culminates in achieving his goal of becoming a professional kishi, a victory shown alongside Shion's own success, indicating his hard-won place in the shogi world. His notable abilities lie in his powerful and determined playing style, honed by desperation and a need to win, which makes him a formidable opponent even against a prodigy like Shion. He is also a gifted player, capable of advancing to final matches in high-level tournaments early in his career.