Hitomoji Kobayashi is a male classmate of the protagonist, Megumi Amatsuka, and a key member of the group that forms around her. He is a young man with an old-fashioned, stoic atmosphere, but is also notably handsome and tall, making him very popular with the female students at his school. His nickname among peers is samurai, a reference to his strict upbringing and demeanor.

His background is defined by the intense training he received from his grandfather, who raised him to be the strongest samurai living in the modern world. From a very young age, Hitomoji underwent severe discipline to master martial arts to an exceptionally high level. This training has made him remarkably strong, with his pure combat technique surpassing that of his peers, including the brawler Kenzo Soga and even Megumi herself. His personality is characterized by a strong sense of justice, directness, and a strict, stoic nature. Despite his serious and somewhat rigid demeanor, he is not arrogant about his popularity or abilities. He treats everyone equally and kindly, which contributes to his positive reputation.

Hitomoji initially clashes with Megumi, feeling that she is arrogant and needs to be disciplined. However, as he comes to understand her true nature, they become close allies. A turning point in their relationship occurs when Hitomoji helps Megumi retrieve a friend's keepsake from a group of thugs. After their reconciliation, Megumi herself acknowledges him positively, saying he is cool and that if she were a woman, she would fall for him. For his part, Hitomoji always addresses Megumi with the respectful honorific -san. His straightforwardness can be socially awkward, leading Megumi to describe him as a strange kind of good person. His biggest personal flaw is a complete lack of a sense of humor; his attempts at comedy are met with frozen silence from everyone around him. He is aware that his overly serious personality makes him seem dark, and he has sincerely wished for a brighter, more comedic personality.

Within the story, Hitomoji is a consistent presence and a powerful asset to the group informally known as the Megumi-dan. He often acts as a striker in serious situations, and his strength is critical to the group's success in conflicts. Although he is in a different class and sometimes acts alone due to his daily martial arts training, his loyalty to the group is unquestionable. A significant misunderstanding arises when others, including Megumi, interpret his philosophy that "it doesn't matter if you're a man or a woman" as an indication of bisexuality. This is later resolved when it is revealed that his romantic interest is actually directed toward their classmate, Miki Hanakain. In the final stages of the narrative, he comes to realize the depth of his feelings for Miki. His development shows a shift from viewing Megumi with possible romantic interest to surpassing that to deeply respect her as a person, while his genuine romantic affections settle on Miki. A notable, though minor, trait is his eccentric desire, expressed during a magical encounter, to own a legendary sword, which he finds too much trouble to actually acquire.