Jiki is a twenty-year-old fighter belonging to the First Ship of the national defense organization Circus. Standing at 176 centimeters tall with A-type blood, he is characterized by his sharp tongue and a duplicitous nature that is often described as black-hearted.

On the surface, Jiki presents himself as a soft-spoken and good-natured individual, especially when interacting with strangers or ordinary people. However, this pleasant demeanor is largely a facade. When among familiar colleagues or those who irritate him, he frequently makes snide and hurtful remarks that seem to reveal his true, more truthful thoughts. This tendency towards cruelty is so pronounced that it even provokes a deep-seated wariness in the young protagonist Nai, whose animalistic instincts sense danger from Jiki, causing him to refuse to be alone with him for a considerable time. Despite this cold and sometimes mean-spirited personality, Jiki has a surprisingly sociable side, though he tends to keep his interactions superficial. He enjoys cultivating medicinal plants and collecting herbs, a hobby he pursues with genuine interest. He has a notable dislike for junk food, preferring dishes such as landmarl meunière.

Jiki’s motivations are primarily driven by his romantic feelings for his colleague, Tsukumo. He constantly seeks her affections, though his attempts are almost always thwarted by Iva, another First Ship member who shares an intense rivalry with him over Tsukumo. Iva views Tsukumo as an innocent little sister to be protected, while Jiki’s desires are more directly romantic, leading to frequent conflict. This rivalry extends to a general dislike for Iva, whom he finds difficult to deal with. He also looks down on Gareki, partly because Tsukumo shows a fondness for the boy, even making him a plush doll, which fuels Jiki’s resentment. He struggles to handle his superior officer, the easygoing and unreserved Director Suoh, whom he often criticizes sharply. While he frequently bickers with his fellow First Ship member Kiichi, the two form an effective combat team.

Within the story of Karneval, Jiki serves as a combatant for the First Ship. His role becomes more prominent when his unit is tasked with protecting Nai. In battle, he wields a whip with extreme efficiency as his primary weapon. Jiki’s most defining physical trait is his eyes, which can capture and process light far better than a normal person’s, granting him exceptional vision that allows him to see even the faintest reflections of minuscule objects. This ability is so powerful that bright light can be overwhelming for him, forcing him to wear glasses at all times to tone down the radiance. In serious combat situations, he removes his glasses to unleash his full visual capabilities. Complementing his unique vision, Jiki possesses the ability to control insects for combat and can create powerful illusions. His special techniques include Leleti (Joyful Blindness), which summons a large insect to aid him in battle, and Champunerungu (Insect's Recollection), an ability that allows him to suddenly disappear from sight. A minor but notable detail about his appearance is that his original hair color is grey, which he frequently dyes black.