The heir to the Gero family, one of the five great clans of "Users" and masters of poison. He is a top-tier assassin. Because he has lived his life in the underworld, he has zero experience with romance and is awkward around women. He starts job-hunting for a marriage partner out of necessity to carry on his family line. His hobbies include collecting toy snacks, and he relieves stress by cleaning. Appearance: A calm atmosphere, dark blue hair, and glasses. Attire: A dark gray long coat over a white shirt with a light blue and red gradient collar, black pants, and dress shoes. In combat, he removes his glasses and wears a gas mask. He uses poison-filled syringes taped to his hands or held normally; he also uses them for doping and carries multiple types. He fights using "Jogyokuka PRO" (an acid-based poison) that can melt anything, as well as hand-to-hand combat.

A master marriage swindler who boasts they can seduce almost anyone, regardless of gender, in 30 seconds. They serve as Hikaru's marriage hunting advisor. At first glance, they appear to be a beautiful woman, but they are male. After meeting Gero, they end up helping him with his marriage hunt through an unexpected turn of events. They love delicious food and are a surprisingly big eater despite their appearance. Appearance: Long blonde hair with pink gradients at the tips. They have beauty marks near their eye and mouth. Attire: A white flare dress with a cinched waist, featuring a black collar and a floral ribbon tie. Wears black tights and brown loafers. Cannot fight.

A "Hamster User" from a branch family of the "Beast Users." Her partner Sirius (a hamster) excels at intelligence gathering. She has a cheerful personality. Gero saved her in the past, leading her to become a secret fan who quietly roots for him. She usually works at a small-to-medium advertising agency. She is searching for her long-lost brother. Appearance: Long pink hair with white mesh in the bangs. Wears star-shaped earrings and a red choker. Attire: A pink bustier with glasses hanging from the neckline, a white outer jacket worn off the shoulders, a bordeaux tight skirt with a deep slit, and black short boots. Incapable of direct combat, but excels at information gathering using Sirius. She is protected by Hikaru.

A phantom thief who works to reclaim unjustly stolen artworks and return them to their rightful owners. She has high communication skills and can become friends with anyone, but she doesn't talk much about herself. She loves sharks dearly and collects shark merchandise and movies. Appearance: Characterized by orange short hair and refreshing blue eyes. Attire: A black high-neck inner shirt and black leggings with red lines on the thighs, topped with a blue denim jacket and white sneakers. Incapable of combat; she focuses on stealing back stolen art for restitution and is protected by Hikaru.

A "Water User" and a businessman in the underworld. He has a very business-like personality and carries out his work thoroughly. He is always clad in a diving suit. Appearance: Short light-blue hair and sharp, scornful eyes. Wears large hoop earrings. Attire: A navy-based form-fitting suit with yellow lines. The arms have white, loose sleeves, and the outfit is an active style integrated down to the matching footwear. In combat, he manipulates water. He used to suffer from a "Clear Air Allergy," but it was completely cured with the help of his former enemy, Hikaru Gero.

A college student and the next president of Balzac Inc., a major corporation with a party goods brand valued at 1.5 trillion yen. She is shy and constantly worries about others' feelings, a trait she dislikes and wants to change. Her hobby is magic tricks, as she loves making people happy. Incapable of combat; she is protected by Hikaru.

A civilian, but a mutation who possesses strength exceeding that of a "User." He has exceptionally high information processing capabilities and superhuman athletic ability. He doesn't perform well unless he sleeps at least 10 hours a day, but most injuries and ailments heal once he sleeps. In terms of raw talent as an assassin, he is one of the best in the modern era. In combat, he utilizes his extreme processing speed and athleticism while using knives. However, he cannot recover without his 10 hours of sleep. He was once an enemy, but joined forces with Hikaru when their goal of defeating the Beast Users aligned.

A descendant of the single-lineage "Sound Users." He has a unique vibe and a habit of adding the word "Do-" (Extreme) to his vocabulary. He is incredibly handsome and popular with women. Since his techniques require relaxation, he has invented numerous original relaxation methods. Appearance: Long straight blonde hair. A small tattoo on his neck. Attire: A black three-quarter sleeve shirt with a wide neckline, gray sweat-style pants, and zori sandals. In combat, he can deliver invisible, powerful shocks and attacks using sound waves as a medium. For some reason, he sometimes fights shirtless, making him a bit of a weirdo. An enemy targeting Shiori's life.

The fourteenth son of the main Dogo family, one of the five great clans and "Beast Users." He possesses the "Beast Blood" of a bat. An elite biotechnology researcher who was appointed head of the Dogo research institute at age 10. He is currently almost entirely estranged from the main family. Appearance: Pinkish hair styled in a slicked-back look. Wears sunglasses, bracelets on both arms, and rings. Attire: A white zip-up jacket with fur at the collar, black track pants with yellow side lines, and white shoes. In combat, he can create "Synthetic Beasts," special creatures with immense power. An enemy.

A descendant of the "Divers" under the Beast Users' umbrella. She uses unique techniques different from other Beast Users. She is a 3rd dan in Beast Karate. Appearance: A blonde short bob with cat ears, and her eyes are covered with white bandages. She wears a choker with a key attached. Attire: A classic long black-and-white maid dress with a bold open chest. A formal yet distinctive outfit paired with a headdress, black gloves, and black tights. In combat, she utilizes karate techniques. An enemy.