Hiromi Iwasa is a student at Sekei High School and a supporting character in the story, known for his unique and artistic approach to tennis. He is a quiet and introspective young man with a deep passion for reading books and painting, a side of him that emerges with noticeable excitement whenever the topic of art is discussed. His physical appearance is that of a teenage boy with brown hair, black eyes, and he is often seen wearing glasses.

Iwasa's primary motivation for playing tennis is inextricably linked to his love for painting. His parents did not support his desire to become an artist, so he took his creative impulse to the tennis court, treating matches as a canvas for his works. This unusual motivation defines his entire playing style. Rather than focusing on countering an opponent's strategy or simply winning points, Iwasa constructs rallies with the specific goal of creating a visual composition with his shots. He is considered an expert in change-of-pace strategies and is an instinctive player, similar in that regard to Natsu Takasaki. For example, during a match, he aimed to draw Van Goghs Avenue of Poplars by using a series of precisely placed lobs. His attacks are governed by the picture he wants to draw rather than a reaction to his opponent, making his tennis highly unorthodox and difficult for logical players like Eiichiro Maruo to read.

In the story, Iwasa serves as a notable opponent for the protagonist, Eiichiro Maruo. He enters as the third seed in the second Kanagawa Junior Tennis Circuit, where the two face each other in the quarterfinals. Iwasa has a peculiar habit of not researching his opponents before a match. Instead, he learns and draws an image of them while they are playing on the court, a method that initially confuses Eiichiro. Their match becomes a significant challenge for Eiichiro, who struggles to comprehend Iwasas patternless, instinctual style. Despite pushing himself to a level of seriousness he had never reached before during the match, Iwasa ultimately loses due to a cramp, having pushed his body beyond its limits. The match is an anti-climax for Eiichiro, who expresses a desire to play Iwasa again under better circumstances.

Following his loss, Iwasa experiences a key moment of development. He decides to step back from competitive tennis after graduating from high school to focus on his true passion of drawing on a canvas. After the match, he asks Eiichiro why he plays tennis, and is surprised by Eiichiro's answer, showing a brief but genuine curiosity about the different paths athletes can take. His key relationship is with Eiichiro, built entirely on their competitive encounter, which forces both characters to confront their fundamental reasons for playing the sport. In terms of notable abilities, Iwasa is an all-rounder whose greatest weapon is his change-of-pace strategy used to create drawings on the court. Because his attacks are based on artistic whim, opponents find him extremely difficult to anticipate. It is suggested by Eiichiro that if Iwasa were to focus seriously on becoming a professional tennis player instead of treating the court as a sketchpad, he could become a much more dangerous competitor.