Hitomonji Kobayashi is a central supporting character in the comedic narrative, serving as a classmate to the protagonist. He is a young man with an old-fashioned and dignified atmosphere, characterized by his tall stature, handsome features, gray eyes, and black hair cut to ear length. Initially, he presents the image of a cool and popular student, admired by many of his female peers, which in turn generates a significant amount of envy and animosity from the male students.

Beneath this polished exterior, Kobayashi possesses a personality marked by seriousness and an inflexible, rigid adherence to his own principles. His background reveals that he has undergone strict modern warrior training under his grandfather, which accounts for his exceptional physical strength and combat skills. This upbringing instilled in him a strong, traditional moral code. At the outset of the story, he views the protagonist's boisterous and unrefined behavior as low-class, but his perception changes when he discovers a more noble and selfless side to her character after she performs a kind act for him without seeking recognition.

Kobayashi’s role in the story is multifaceted. He often acts as a straight man who unintentionally breaks the mood due to his inability to be flexible, yet his seriousness becomes a crucial asset in more dangerous situations. He is an unofficial but vital member of the group of friends who surround the protagonist, providing muscle and strategic thinking during fights. Despite claiming to only seek a quiet place to read, he is frequently found at the hangout spot of the protagonist's self-proclaimed protection squad, suggesting a camaraderie he refuses to openly acknowledge.

Key relationships define his development, particularly his evolving bond with the main character. After an initial period of wanting to discipline what he saw as arrogance, he grows closer to her, especially after helping her recover a precious item from thugs. A notable and humorous aspect of his character involves a significant misunderstanding stemming from his old-fashioned speech. When he once stated that a person's gender does not matter, several of his friends, including the protagonist, mistakenly believed he was confessing to being bisexual. This misunderstanding is eventually cleared up when it becomes evident that his romantic interest lies with a different female character, Miki Hanakain.

Kobayashi demonstrates remarkable abilities that are nearly superhuman. He is shown to be stronger than several of his other physically capable peers and possesses immense durability and skill in combat. Examples of his prowess include defeating a spearman using only a single brick, catching a brick thrown by an adult with his bare hands, and continuing to fight successfully even after sustaining severe injuries from bladed weapons. However, he also possesses a notable and consistent weakness: his complete lack of a sense of humor. Any attempts he makes at telling jokes or being funny are met with literal silence and a frozen atmosphere from everyone around him, a trait that reinforces his otherwise serious and inflexible nature.