Naoki Yamanashi is a supporting character in the anime Opus.COLORs. He is the father of the protagonist Kazuya Yamanashi. Naoki was a pioneer in the field of perception art, a sensory-based artistic movement that became central to the world of the series. Together with his wife Akari Yamanashi, as well as Togo and Yua Takise, the parents of Kyo Takise, Naoki helped lay the foundation of perception art and became a highly respected perception artist in his own right. He died young in an accident that occurred ten years before the main events of the story, but his legacy endures; he is remembered and revered by later artists as the originator of perception art.

Naoki is described as a gentle and kind father. His calm and warm demeanor made him a supportive presence in his son's life, and his personality is remembered fondly by those who knew him. He had a close personal history with the Takise family: he was childhood friends with Yua Takise and met Togo Takise during their time together at art school, becoming close friends. These bonds connect the central characters in the present day.

Naoki's primary motivation appears to have been the development and advancement of perception art, a pursuit he shared with his wife and friends. His role in the story is largely as a deceased figure whose influence and ideals continue to shape the goals and conflicts of his son Kazuya and those around him. His life's work established perception art as a respected discipline, and his sudden death created unresolved emotional weight that affects key relationships, particularly between Kazuya and Kyo.

Notably, Naoki's abilities were artistic and intellectual rather than supernatural. As a perception artist, he possessed the talent to create immersive works that engage multiple senses, a hallmark of the movement he helped pioneer. His contributions to this art form remain influential long after his passing, and he is regarded as a foundational figure in the perception art world.