Haruya Nanjo is a secondary character and an upperclassman who is one year older than the protagonists Kyotaro Ichikawa and Anna Yamada. He is well-known throughout the school, primarily for his flashy and persistent behavior, particularly his repeated attempts to pursue Anna, a popular model. Ichikawa frequently refers to him with the dismissive nickname Nanpai, which combines his surname with the honorific for senior.

In terms of appearance, Haruya sports a fashionable and distinctive hairstyle featuring dyed blonde hair with the underlayer near his ears left in its natural black color. His character design is deliberately simple; his eyes are often drawn with basic pupils that appear as circular lines, contrasting with the more detailed features of the main cast.

His personality is defined by a forceful and unwavering persistence, especially when he sets his sights on a girl he finds attractive. Haruya is a suave and confident individual who attempts to use compliments and pickup lines to gain attention, though his efforts are met with mixed success. He is skilled at steering conversations to suit his own agenda and can be oblivious to social cues, rarely backing down unless he is directly and firmly rejected. His motivation for chasing Anna appears to be rooted mainly in her looks and social status, but a deeper, genuine interest is also suggested. While his demeanor often paints him as a shallow playboy destined to be a recurring source of annoyance, there are suggestions that his outgoing and frivolous behavior might be a mask to hide his true feelings or past insecurities.

Within the story, Haruya serves as a recurring source of tension and a rival to Kyotaro, acting as a catalyst that pushes the protagonist to confront his own feelings for Anna. While he is often perceived as an antagonist due to his persistent advances and the fact that the narrative is largely filtered through Kyotaro's jealous perspective, Haruya is not portrayed as a malicious individual. This complexity is highlighted during a significant incident where Kyotaro, frustrated, throws his bicycle into a river. Haruya is the first to step in and help retrieve it, demonstrating a surprising and genuine capacity for kindness and altruism.

His key relationships are predominantly defined by his interactions with the main group. His main target is Anna Yamada, but all her friends, particularly one named Moe, distrust him, see him as a bad influence, and consistently block his advances. He is sometimes described as polygamous due to the other girls he hangs around, a trait that further cements his reputation. His relationship with Kyotaro is one of rivalry, though it is one-sided. Kyotaro views him as a threat, but Haruya has shown he is willing to help even his rival when the situation genuinely calls for it. This duality causes his presence to influence Kyotaro's actions, often prompting Kyotaro to be more assertive in his own relationship with Anna. One of the most notable scenes showcasing this dynamic occurs when Anna, tired of Haruya's advances, pretends to kiss Kyotaro in front of him, effectively and humorously ending his pursuit in that moment.

Regarding his background, it is known that Haruya was once a member of the soccer club. He stopped playing due to an injury and a subsequent belief that he could not succeed at the sport, a detail that adds a layer of unfulfilled ambition to his character. His notable abilities are primarily social; he is well-liked enough to have a group of friends, is good at manipulating conversation, and shows no fear in pursuing what he wants despite repeated failures. Ultimately, while he is often portrayed as pushy and annoying, his actions also serve to make the story more interesting and inadvertently support the growth of the main couple.