Kakugari, whose real name is Hiroyuki, is a recurring character in Urusei Yatsura. He is a classmate of the protagonist Ataru Moroboshi and one of the four core members of an informal group known as Lum's Stormtroopers, a fan club devoted to the alien girl Lum. His nickname, Kakugari, is a Japanese word for a crew cut, which directly refers to his most distinctive physical feature: his short, closely cropped hairstyle. He has a large, stout, and muscular build, making him the physically largest and strongest member of the Stormtroopers, and he is typically seen wearing his Tomobiki High School uniform. His appearance is completed with brown hair and black eyes.

Personality-wise, Kakugari is depicted as the most temperamental and ill-tempered of the group, often acting as its primary enforcer and bodyguard. He is quick to use his physical strength to bully others on behalf of the Stormtroopers, with his most frequent target being his fellow member, the small and often-whipped Chibi. Despite his aggressive demeanor, his role is often limited, and he is considered the least used or important of the four Stormtroopers. Like his friends, he is obsessively devoted to Lum, and his primary motivation is to see her happy, which he believes requires separating her from the unfaithful Ataru. This devotion is, however, entirely self-serving, as all the members secretly hope to win Lum's heart for themselves. This creates a dynamic where they work as a group against Ataru but will not hesitate to turn on and betray one another if they perceive a chance to gain Lum's favor. Outside of their shared obsession, they engage in typical otaku culture, such as enjoying science fiction, films, and manga.

In the story, Kakugari serves as background comic relief and part of a collective antagonist force that harasses Ataru and worships Lum. His key relationships are primarily with the other Stormtroopers. He often acts as the muscle for the group's de facto leader, Megane, using his larger build to help with physical tasks and intimidation. His most notable and volatile relationship is with Chibi, whom he constantly bullies and puts in chokeholds, making Chibi the usual recipient of his violent temper. While he is closest to Chibi among the group, their friendship is highly unstable.

The character's development in the source material is minimal. His real name, Hiroyuki, was only revealed in the final episode of the original anime series and in supplemental materials like the Shonen Sunday Graphic magazine. In the original manga, Kakugari and the other Stormtroopers (with the possible partial exception of Perm) disappeared early on, and their roles were often given to other characters. As a result, his character was never elaborated upon in the manga compared to the anime, where he remained a mainstay. Notably, Kakugari was the only member of Lum's original Stormtroopers to be entirely excluded from the 2022 remake of the anime for unknown reasons. His most notable ability is his physical strength, which he primarily uses for bullying, though it is rarely effective against the super-powered characters like Lum or Ataru. The group, including Kakugari, has also made a cameo appearance in another work by Rumiko Takahashi, appearing as a gang of local hoodlums in an episode of the anime series Yashahime.