Akito Hayama emerges as a disruptive force in his sixth-grade class, ruling through intimidation and blackmail while maintaining a cold, aloof exterior. His troubled background originates with his mother's death during his birth, causing resentment from his older sister Natsumi – who frequently called him "devil boy" – and emotional neglect from his work-absorbed father, Fuyuki. This familial rejection resulted in isolation; Akito often ate alone and spent hours wandering the streets to avoid home.

Early behavioral issues surfaced around age five. He became closed-off and disruptive at school to cope with his home life. Despite his delinquency, he maintained strong academic performance and possessed notable physical strength, particularly in martial arts. A turning point occurred when classmate Sana Kurata confronted him, using blackmail tactics mirroring his own to curb his behavior. Through Sana's persistent efforts, Akito's family dynamics gradually improved. This culminated in a pivotal moment where Sana role-played as his deceased mother to convey the message, "I love you, that's why I gave birth to you," helping alleviate his longstanding guilt.

Akito's personality blends outward stoicism with intense loyalty. He adheres to a personal code of honesty, refusing to lie or feign respect for those he dislikes. Though verbally reserved, he expresses care through actions, using the phrase "I don't hate it" to signify deep affection for sushi, dinosaurs, skiing, and eventually Sana. Their relationship evolved from rivalry to romance, though it faced complications when Akito briefly dated Fuka Matsui during Sana's absence, creating a love triangle. This resolved when Fuka acknowledged Akito's enduring feelings for Sana.

Significant character development occurred through multiple traumas. He sustained a near-fatal arm injury while preventing a classmate's suicide, resulting in temporary paralysis and an out-of-body experience where he communicated with his deceased mother, reinforcing his will to live. Later, his move to America for medical treatment triggered Sana's emotional collapse, though their separation ultimately strengthened their commitment. Akito returned to Japan as a skilled karate practitioner.

In the sequel "Deep Clear," adult Akito works as a doctor and marries Sana. When she becomes pregnant, his unresolved trauma surfaces, fearing her potential death during childbirth like his mother. He demands a divorce if she continues the pregnancy, leading to separation. They reconciled during Sana's labor, ultimately welcoming a daughter named Sari.

Notable traits include acrophobia (fear of heights), a preference for blue clothing, and close bonds with childhood friend Tsuyoshi Ohki – the only person able to calm Tsuyoshi's rage episodes through a signature karate chop.