Hikaru Gosunkugi is a recurring character who appears as a classmate of Ranma Saotome and Akane Tendo at Furinkan High School. He is a student of around sixteen years of age, noted for his gaunt and unhealthy appearance, which is most recognizably defined by the permanent dark circles under his eyes, a hereditary trait shared with his parents. His physical frailty and lack of presence make him one of the least popular and most overlooked students at the school.

Personality-wise, Gosunkugi is characterized by his extreme shyness, pessimism, and a somber disposition. He is deeply insecure, acutely aware of his own physical weakness, and possesses a strong sense of inferiority when compared to more powerful figures like his rival, Ranma. Despite his timid nature, he harbors a persistent and obsessive love for Akane Tendo, though he is far too shy to ever express his feelings directly. This unrequited affection is his primary motivation, driving him to devise numerous schemes to eliminate his romantic rival. While he often resorts to underhanded tactics and strange plots born from jealousy, he is not entirely malevolent and has occasionally shown moments of genuine gratitude, particularly towards Akane when she inadvertently helps him.

Gosunkugi's primary role in the story is that of a comic antagonist and minor rival to Ranma. Lacking any martial arts skill, he cannot compete physically with Ranma, Ryoga Hibiki, or Tatewaki Kuno. Instead, he relies on a self-taught, mystical fighting style he refers to as Japanese voodoo. His signature techniques involve nailing straw effigies to trees with a wooden mallet, often missing and striking his own thumb, and performing rituals with lit candles tied to his head. He is also a skilled photographer, a talent he uses to secretly take pictures of Akane. He sells these photographs to Tatewaki Kuno, who hopes to find a weakness in Ranma. Through this arrangement, Gosunkugi eventually discovers Ranma's debilitating fear of cats (ailurophobia), though his subsequent plan to exploit this weakness ultimately fails.

His key relationships are defined by his obsession with Akane and his rivalry with Ranma. Ranma hardly views Gosunkugi as a serious threat, often playing friendly jokes on him or inadvertently saving him from bullies, which creates a dynamic of one-sided animosity from Gosunkugi. He also has a transactional relationship with Tatewaki Kuno, serving as his paid informant and photographer. In the anime adaptation, Gosunkugi has a larger role, and in one episode he briefly falls in love with a ghost girl named Kogane, who reciprocates his feelings before she must depart at the end of the summer festival.

In terms of development, Gosunkugi remains a perpetually unsuccessful schemer. While he believes himself to be a master of disguise, his attempts are always transparent and only serve to embarrass himself. On one notable occasion, he purchased a high-tech suit of powered armor called the Warsuit to physically challenge Ranma. However, the suit was rigged to explode unless the wearer defeated their rival. True to his pride, Ranma refused to let Gosunkugi win, and the subsequent explosion engulfed them both, leaving the scheme in ashes. His role is more prominent in the original manga, where he appears frequently throughout the series. In the anime, many of his narrative functions, such as serving as Kuno's spy, were transferred to an original character named Sasuke Sarugakure, delaying Gosunkugi's own anime debut until much later in the series.