Masami Shibata, affectionately called "Maa-chan" by Atsushi Arisawa, spent his childhood in Norway with his Japanese father and Norwegian mother. Following his mother's death during his youth, his father relocated the family to Japan while running a business, leaving Masami to often care for his younger brother Masayoshi. This shared loss forged an unbreakable bond between the brothers. Masami later taught at Jougaouka High School, tutoring Atsushi; his kindness there sparked the boy's childhood crush.

Gentle, thoughtful, and reserved, Masami's personality contrasts with his brother's. After retiring from teaching, he lived quietly but grappled with deep-seated personal challenges stemming from past trauma. A sexual assault during his teenage years led him to believe he was "defiled forever," severely impacting his self-worth and relationships. This caused him to avoid physical intimacy and struggle with feelings of unworthiness, particularly with his partner, Jougaouka math teacher Tooru Hagiwara.

Masami initially kept his relationship with Tooru hidden, burdened by internalized shame and fear of rejection, especially from his family. His father accidentally discovered their relationship and reacted with disapproval, reflecting traditional views. Masami's path to acceptance involved confronting his trauma through intimate psychotherapy sessions with Tooru, who steadfastly reassured him his past did not define him. This process enabled Masami to gradually overcome his insecurities and embrace closeness.

Family dynamics significantly influenced Masami. His fiercely protective brother Masayoshi saw Tooru as a threat to their bond, creating tension. Masami worked to balance his loyalty to Masayoshi with his commitment to Tooru. Eventually, their father accepted Masami's relationship, attending his and Tooru's wedding and offering emotional support despite earlier objections. Masami's grandmother, while not fully endorsing the union, acknowledged its sincerity and gave a conditional blessing, likening it to Masami's father's unconventional marriage.

Masami also navigated societal pressures, rejecting an arranged marriage proposal to model Mizhua Toda to remain with Tooru. He supported Atsushi's evolving feelings for Masayoshi, transitioning from Atsushi's childhood object of admiration to a mentor figure. His wedding to Tooru symbolized his healing and acceptance of his identity.

Throughout his story, Masami's quiet strength and resilience are evident. He evolved from a withdrawn individual burdened by shame into someone capable of sustaining a committed relationship and advocating for his own happiness. His interactions with his father, brother, and partner illustrate a journey toward self-forgiveness and familial reconciliation.