Hoshi is a resident of the community living under the Arakawa River bridge, known as a musician who frequently performs with his guitar along the riverbank. At twenty-four years old, he stands 179 centimeters tall. His defining physical characteristic is the large star-shaped headpiece he almost always wears, a choice that led the community’s leader, the Village Chief, to give him the name Hoshi, which means star in Japanese. Beneath this star mask is a second mask shaped like a moon; he only reveals his true face, that of a young man with reddish-brown hair, when he ventures out to the bridge and the world above.

Hoshi’s personality is defined by passion, flair for the dramatic, and a deep-seated yearning for authenticity and recognition. He is a heavy smoker with a particular fondness for a specific brand of cigarettes and possesses a keen sensitivity to fashion and personal style, often acting as an impromptu stylist for his neighbors. In the past, he was a highly successful pop star with chart-topping records, but he became disillusioned after a tabloid scandal involving a romantic relationship. When his girlfriend distanced herself from him to protect her own career, Hoshi was deeply hurt and felt his musical talent was a hollow fabrication of the industry. This crisis led him to Nino, whose otherworldly perspective inspired him to abandon his commercial success. He chose to live under the bridge, donning his star mask as a symbol of his new identity as a true artist creating his own music, no matter how strange or unpolished his songs might be.

A central aspect of Hoshi's role in the story is his unrequited love for Nino, the Venusian girl who saved the protagonist Kou. This romantic rivalry with Kou is the primary source of much of the community's comedic conflict and Hoshi's personal frustration. He frequently schemes with other residents, like the militaristic Sister, to interrogate Kou or disrupt his relationship with Nino, often leading to embarrassing defeats. Hoshi is deeply jealous of Kou's position as Nino's official lover and constantly seeks to prove himself as a superior partner, though his feelings for Nino are generally not reciprocated or even fully acknowledged by her.

Despite their rivalry, Hoshi and Kou share moments of unexpected camaraderie and often find themselves on the same wavelength, finishing each other's sentences or sharing similar logical yet absurd trains of thought. This dynamic makes their conflict more than simple animosity, revealing a strange respect and kinship between the former corporate heir and the fallen pop star. Hoshi's key relationships are thus defined by this tense yet humorous triangle. He is also a well-integrated member of the wider community, participating in group activities like star-gazing parties, though his obsessive nature often turns simple events into chaotic but heartfelt affairs.

Throughout the series, Hoshi undergoes a subtle but significant development. While he begins as a man who has run away from his painful past in the music industry, his time under the bridge allows him to slowly reconcile with his own ambitions. He remains a rival to Kou but eventually accepts the young man's place in Nino's life. By the story's conclusion, Hoshi is able to leave the bridge community, discarding his star mask and returning to the world above to hold a successful comeback concert, finally achieving artistic fulfillment on his own terms. His notable abilities include playing the guitar and composing music, though the quality of his lyrics is often called into question. He also possesses unexpected practical skills, such as the ability to cook Italian dishes, and is strong enough to handle the physical rigors of life along the riverbank.