Kurourushi.

History
Kurourushi is one of the sixteen registered Special Grade Cursed Spirits. He was born from humanity's collective fear of cockroaches. At some point, he was captured and absorbed by Kenjaku (using Suguru Geto's Cursed Spirit Manipulation Technique). Kenjaku releases him during the Defeat Game so he can participate as a player in the Sendai Colony.
There, he accumulates 54 points by consuming humans and curses. He faces several strong characters, such as Takako Uro (whose arm he cuts off, and who considers him a bad matchup due to his fighting style), Ryu Ishigori, and finally Yuta Okkotsu. Yuta exorcises him in combat, gaining points in the process. However, even after his "death," Kurourushi regenerates or is reborn through his offspring (by parthenogenesis), as the cursed energy of his persistent fear of cockroaches passes to his "child," allowing his return.

Personality
Kurourushi is a pure cursed spirit, devoid of morals or complex human emotions. He is extremely predatory, vicious, and sadistic. He loves the taste of blood (literally saying, "I like the taste of iron"), and his behavior revolves around hunting and devouring. He displays no loyalty or engages in deep dialogue; he is rather instinctive and brutal, focused on survival and consumption. His repulsive nature and his swarm-based attacks make him one of the most disgusting and feared cursed spirits in the series.

Kurourushi (Japanese: 黒沐死, Kurourushi) is a special-grade cursed spirit in Jujutsu Kaisen, known for being a cockroach-based cursed spirit. It primarily appears in the Culling Game arc.

Appearance
Kurourushi has a grotesque appearance, clearly inspired by a humanoid cockroach. He is quite tall and composed of a light-colored, insect-like exoskeleton. He can generate up to four human-like arms and possesses human hands and feet. His abdomen, wings, and limbs are covered by a black shroud-like structure that extends from his head and opens when he moves or attacks. His face is particularly repulsive: it features six long antennae and eight eyes, evoking the typical ugliness of a cockroach. Overall, his design is disturbing and gives the impression of a giant insect with anthropomorphic features.