Masayuki Haitani is one of two close friends of the protagonist Keitaro Urashima, both of whom he knows from the Sasagi seminar preparatory school. As a fellow ronin, or student who has failed college entrance exams, Haitani is a second-year repeat examinee. He is physically distinct from his friend Kimiaki Shirai, being tall and lean with smaller glasses than either Shirai or Keitaro. His brown hair reaches approximately shoulder length, and his eyes are black.

Haitani possesses a relaxed and confident demeanor, often giving the impression of someone simply looking to enjoy himself. His personality is defined by a playboy attitude, as he is frequently on the lookout for attractive women and enjoys spending his time pursuing them alongside his companion Shirai. Despite this tendency to appear shallow, he has a more steadfast and supportive side, particularly in his friendship with Keitaro. When Keitaro becomes lost in his daydreams or overly complicated by his own romantic struggles, Haitani is often quick to heckle him, but he is also a reliable friend who helps bring Keitaro back on track when necessary.

Haitani’s primary motivation is to enjoy life and, initially, to successfully pass his university entrance exams. While he and Shirai frequently attempt to pick up girls and socialize, they also contend with the pressures of being ronin. Although Haitani is initially described as having only a twenty-five percent chance of getting into his first-choice school, he ultimately succeeds in his academic goals, passing his exams after Keitaro fails and becomes a third-year ronin. He and Shirai fill the role of comic relief and supportive sidekicks within the larger narrative. They often appear unexpectedly to provide commentary on Keitaro’s situation, offer misguided advice, or attempt to set him up with Naru Narusegawa, the female lead, though their plans frequently backfire. For example, one such attempt causes Naru to become angry with Keitaro until Haitani apologizes. They also serve as a connection to Keitaro’s life outside the Hinata Inn, appearing for events like working at a beach cafe or taking part-time jobs during Christmas.

Haitani’s most significant relationship is with his best friend, Kimiaki Shirai. The two are almost always seen together, functioning as a comedic duo. They are both students at the same prep school and share similar interests in chasing girls and teasing Keitaro. However, a running gag in the series is that the main residents of Hinata Inn frequently forget who Haitani and Shirai are whenever they appear. Despite this, they are considered friends of the family and are even invited to Keitaro and Naru’s wedding, though Haitani cannot resist attempting to flirt with Motoko’s married sister, Tsuruko, at the ceremony. In their interactions with the wider cast, they often find themselves on the receiving end of slapstick violence, such as when Motoko Aoyama unleashes a ki attack on them after Haitani tries to make a pass at her.

In terms of development, Haitani’s primary arc is his academic journey. He begins as a struggling ronin alongside Keitaro but manages to pass his exams and move on from the preparatory school life. His loyalty as a friend is also a consistent trait that develops further, as he repeatedly helps Keitaro, even after his own success. On one occasion, he gives Keitaro tickets to a theme park in hopes of facilitating a date with Naru. On another, he helps Keitaro search for a Christmas present for Naru. In a later instance, when Keitaro disappears to take an overseas expedition job, it is Shirai and Haitani who are interrogated by the Hinata residents about his whereabouts, highlighting their close connection to him. He notably has a simple magic trick where he can make a flower appear in his hand, a skill he is fond of using in his attempts to impress girls.