Akito Hayama entered the world on October 12, the son of Fuyuki and Koharu Hayama. Koharu died giving birth to him, plunging the family into dysfunction. His older sister Natsumi blamed him for their mother's death and subjected him to verbal abuse. Grief and work consumed his father Fuyuki, leaving Akito isolated and emotionally withdrawn, burdened by guilt.

As a disruptive sixth-grade student, Akito ruled his classroom through intimidation and blackmail, his cold demeanor earning fear and resentment. Sana Kurata challenged him, using his own blackmail tactics to subdue his behavior. Their adversarial dynamic shifted when Sana learned of his traumatic past. She intervened, forcing his family to confront their mistreatment, leading to gradual reconciliation.

Akito embodies stoicism and emotional restraint, adhering to a personal code of honesty—he refuses to lie or feign respect. He rarely expresses affection directly, using the phrase "I don't hate it" to convey positive feelings toward sushi, dinosaurs, skiing, and eventually Sana. Despite his reserve, he exhibits fierce loyalty and protectiveness toward close friends like his childhood best friend Tsuyoshi Ohki. Highly athletic, he excels in martial arts but struggles with acrophobia.

His relationship with Sana evolved from rivalry to deep romantic attachment. Though struggling to articulate feelings, his actions—involuntary jealousy, protectiveness, initiating their first kiss—demonstrated his commitment. Misinterpreting Sana's feelings during her acting departure, he briefly dated Fuka Matsui. Fuka ended it, recognizing his enduring love for Sana. His devotion faced another test when his father relocated the family to America for treatment of a severe hand injury. Sana's severe depressive reaction ("Doll Syndrome") to their separation forced Akito to confront his own vulnerability, culminating in an emotional breakdown that helped heal her.

A pivotal moment occurred when Akito intervened to save Kazuyuki Komori, a suicidal classmate. Komori stabbed him during the encounter, causing severe blood loss and temporary paralysis in his right hand. Near death, Akito experienced an out-of-body encounter with his mother's spirit, who reassured him of her love. This reinforced his will to live and deepened his appreciation for Sana.

In "Deep Clear," Akito married Sana and became a doctor. When Sana became pregnant, trauma over his mother's death resurfaced, leading him to demand a divorce to avoid potential loss. After their daughter Sari was born safely, they reconciled, though their relationship retained its argumentative dynamic.