Mio Tokinoya is the younger sister of Shun Tokinoya. An accident three years before the main events caused paralysis from her waist down and resulted in their father's death. This condition necessitates Shun's assistance for her mobility.

She displays pronounced emotional dependence on her brother, frequently experiencing loneliness during his work or other absences. She objects to rehabilitation at a distant hospital, dreading the increased separation it would cause. Her opposition to Shun resuming competitive gaming arises from concern it would lessen his attention towards her.

It is later revealed her inability to walk originates psychologically, not physically. She had physically recovered from the accident but remained mentally incapable of accepting walking. This psychological block arose from her intense need to retain Shun's care and attention, coupled with fear that regaining mobility might lead him to leave her.

During a critical moment, she and Shun wager on his participation in a major tournament: if his team wins, she consents to hospitalization for rehabilitation; if they lose, Shun vows never to see her again. As the tournament advances and his team faces potential defeat, the terror of permanent separation from her brother triggers a breakthrough. She summons the strength to stand with support during the event and conveys a passionate message to Shun via video call.

Following Shun's tournament victory, she honors their agreement by entering the hospital and fully committing to the rehabilitation process. This signifies a significant step in addressing both her physical condition and the underlying psychological factors tied to her dependence on her brother.