Gyokko

Gyokko has a very bizarre and grotesque physiology, taking on the form of a pale white, abstracted, grotesque humanoid figure with a muscular upper torso that has no arms and resembles that of an armless statue growing from a porcelain vase, similar to a djinn. He has multiple infant-like hands that line along his head and back.

Gyokko's face is even more distorted, with large green mouths located where one would expect his eyes to be located, and his actual eyes are located vertically from one another on his face; one eye appearing in the constantly open bottom mouth and the other is seated at the center of his forehead. The daiji for Upper Rank is engraved on his forehead's eye and the daiji for Five is engraved on his mouth's eye.

When in battle, Gyokko can molt and transform into his true form, which bears heavy resemblance to that of a merman. In this state, Gyokko retains his facial features and muscular physique but now possesses a more humanoid body covered in transparent scales akin to a fish. He also grows much larger, attains longer hair, black markings on various places around his body, webbed hands, and a long serpent-like tail in place of his legs.

Gyokko is shown to be an easily excitable demon, constantly fawning over new inspirations for what he deems his "art" or what he finds to be sublime, sometimes even going against his initial impressions. He is easily swayed into euphoria whenever Muzan is involved, trying not only to please him, but finding joy in being decapitated and having his head held by Muzan. Although he was dismayed he would have to work together with Hantengu, he nonetheless reasoned it was fine since Muzan ordered it. He also seemed to be somewhat sardonic and condescending; upon sensing Akaza's presence within the Infinity Castle, he almost let out his inner feelings to the demon about being glad he believed him to be dead before correcting himself mid-sentence, even if Akaza was not fooled by his false support.

Gyokko is also short-tempered, shallow, and arrogant, especially when it comes to things regarding his "art", as seen when he was easily enraged by Muichiro when the latter began to insult and make fun of the quality of his art to the point of bleeding from his blood vessels out of sheer fury, and through his conversation with the Hashira, constantly praised himself as "beautiful" and his work even more so, further reinforcing his arrogant and narcissistic personality and even insulting Muichiro as an "ape" for not appreciating his art.

Gyokko revealed himself to be incredibly petty and jealous, as seen when he attacked and mutilated Hotaru Haganezuka due to his jealousy of the latter's focus and dedication to his work, surpassing his own zeal when working on his own art and made him want to instead make the latter lose his focus and waste time on the swordsmith due to this petty jealousy.

Gyokko has a particularly morbid sense of taste, which was showcased when Doma told him he placed a human head on top of his pots like a plant; although Gyokko was slightly taken aback since the pot was not made with such an intention in mind, he nonetheless approved of such use and decided to use it as further inspiration. The extent of this morbid and violent obsession for his is shown even more when he brutally attacked several swordsmiths and used their corpses to create a "beautiful" piece by stitching their bodies together along with sticking several swords into them.

His extreme sadism was further exposed when he went into great detail of explaining his "artwork"; from the many body parts that stood out, to the built-in "feature" of being able to twist a stabbed sword in order to cause extreme pain and bleeding to one of the mangled swordsmiths, demonstrating he not only left his victims unnaturally alive, but also made arrangements to torture them in public.