Masaki Uehara, a lighthearted and flirtatious high school student, thrives on casual romantic connections, contrasting his earnest friend Takumi. His playful teasing—such as openly flirting with Miyabi, who pines for Takumi—fuels subtle friction within their social circle. A returnee from overseas, his English fluency and cosmopolitan ease reflect his international upbringing, bolstering his outgoing, adaptable charm.

The sequel manga’s "Adult Chapter" follows his university-era summer trip to Hakata with Miyabi and Shuhei, reuniting with Ao and Takumi, reinforcing his enduring ties to the group. A spinoff chapter, "The Beginning of Uehara’s Fun-Filled High School Days," spotlights this period without divulging specific events, while his role across the series remains secondary—offering comic relief and stabilizing dynamics between central characters.

Sporting blonde hair and grey eyes, he maintains a typical high school appearance. Though largely static in the main narrative, his minor growth emerges through group interactions and humorous subplots. The sequel marginally deepens his involvement but retains his position as a peripheral figure.