Atsushi Kitamoto is a high school student and a recurring character who becomes one of the first friends Takashi Natsume makes after his move to a new town. Though initially met with hesitation from Natsume, who fears his unusual abilities might be discovered, they eventually form a friendship. Kitamoto often spends more time with his best friend, Satoru Nishimura, than with Natsume.

He has short brown hair and brown eyes, standing slightly taller than Natsume. He is typically seen in his school uniform—a white collared shirt and grey pants—and wears long coats with a scarf in colder weather.

Kitamoto exhibits a sensible and rational personality, choosing a career as a public servant to support his family over personal dreams. He shows a strong sense of responsibility, often scolding his younger sister, Mana, for actions that might disturb their ill father or strain the family’s finances. He also performs caring gestures, such as pulling a blanket over his sleeping father.

In interactions with friends, he is straightforward, humorous, and carefree, assuring Natsume there is no pressure to spend time together if uncomfortable. He displays a gluttonous side, preferring his lunchbox filled with food rather than arranged creatively. At times, he reflects on his life, recognizing he could have faced loneliness like Natsume and expressing gratitude for his stable family.

His family includes his father, mother, and younger sister Mana, a middle school student. He also has a grandfather, an uncle, and an aunt living by the sea. His father’s serious illness the previous year deeply affected him, strengthening his sense of duty toward his family.

Within the story, Kitamoto serves as a consistent supportive friend rather than a major plot driver. His first interaction with Natsume occurs when he greets him at school; Natsume’s sharp reaction surprises him, but they quickly apologize. Kitamoto later observes that Natsume’s eyes initially seemed emotionless and difficult to read. The next day, a conversation leads him to realize Natsume has had little social interaction.

A significant shared experience involves a youkai confrontation at school. Hearing a struggle, Kitamoto rushes to help but finds only Natsume. Later locked in the school after hours, he experiences a strange disappearance of teachers. He finds a bell lost by the youkai, and his accidental ringing resolves the supernatural conflict. Though he finds the event bizarre and likens it to being deceived by a fox, he dismisses his doubts to ensure Natsume is alright. Walking home, he reflects on Natsume’s calm demeanor and deep desire to remain in his current home, which inspires Kitamoto to contemplate being more honest with his own feelings.

He also participates in a study training camp where a mermaid youkai attacks Natsume in an attempt to steal the Book of Friends.

His most important relationships are with Satoru Nishimura and Takashi Natsume. He is also friendly with classmates Kaname Tanuma, Tooru Taki, and Jun Sasada. With his sister Mana, he maintains a typical sibling dynamic, acting as a responsible older brother who scolds her but ultimately cares for her.

The meaning of his name reflects aspects of his character: "Atsushi" means "deep, true, sincere, history," and "Kitamoto" means "north, base, root, origin, source."

A trivia note exists regarding his school class placement: in the manga, he is initially in the same class as Kaname Tanuma, while in the anime adaptation, he is placed with Natsume and Nishimura, a discrepancy possibly due to the animators assuming he and Nishimura were classmates because they are always together.