Zed O'Brien Birthday: February 29 / Adult / 176cm / 58kg / Type A / Member of Libra / Family: The Count (Biological creator). A merman who is the legitimate successor of the "Big Dipper Blood Battle Style: Shinatobe." He has a polite, formal way of speaking and an upright, cultured personality. He has a pair of antennae on his head (though they do not function as hands; they only show slight movement and have no function). He has foldable fins on both arms and webbing between his fingers, with a dignified muscular build despite his slender frame. As a gill-breather, he cannot breathe in the air without his custom-made tank "Aegir (Reverse Aqualung)," so he usually lives in a large water tank at the Libra office. All related equipment and tanks are custom-made, and the tanks are very rare and expensive. He is also capable of gliding. He has blue skin that feels no warmth and eyes from which emotions cannot be read. While his physique and skeletal structure are close to human, he cannot breathe in the atmosphere without the respiratory device attached to his neck because he breathes through gills. For this reason, he usually spends time in the giant water tank provided in the office. Although his attitude is calm and his behavior is intellectual, the combat abilities he possesses lightly transcend human common sense. He is a human-fish hybrid created for amusement by the Blood Breed "The Count," and is a member of a heterogeneous race capable of acting outside Hellsalem's Lot. After being imprisoned in a deserted mansion and living in solitude, he was taken in by Master Raju Jugei Shizuyoshi and underwent rigorous training. He gained considerable culture by discussing poetry, music, art, science, philosophy, and astronomy with the Count. He holds great respect for his master and wishes to become stronger. With his master's help, he decided to step out of his imprisoned tank on his own, and later joined Libra during "Z's Longest Day." He is a fellow disciple of Zapp Renfro under the same master, but their relationship is very poor. He loathes Zapp's violent and vulgar behavior and does not respect him as a person, but he cooperates in crisis situations and acknowledges Zapp's genius. Zapp calls him "Fish" or "Sea Creature," while he usually addresses Zapp as "You." He maintains a polite attitude toward people other than Zapp. He calls Leonardo Watch "Mr. Leonardo" and Gilbert F. Altstein "Mr. O'Brien." He has no consciousness of eating his own kind; he dislikes raw fish but eats cooked fish. He is nearsighted. He once tried to find a job because of something Zapp said but was rejected by both humans and the Alterworld; currently, he earns money by performing origami using the blood technique "Shinatobe: Wind Weaving" in front of the fountain at Andantal Plaza. He is sincere and responsible enough to treat his Libra colleagues to a meal.

Zapp Renfro A cheerful man with silver hair and brown skin. A user of the Big Dipper Blood Battle Style "Kagutsuchi" (Fire attribute), which allows him to manifest various objects like blades using his own blood as a medium and cause them to ignite or explode. He uses an oil lighter as a catalyst to draw blood and ignite it, and he possesses genius combat sense and blood technique operation skills. He is a fellow disciple of Zed O'Brien under the same master, Raju Jugei Shizuyoshi. He calls Zed "Fish" or "Sea Creature" and teases him relentlessly. Unlike Zed, he has a violent, vulgar, and reckless personality, so the two get along very poorly. Zed does not properly acknowledge Zapp as his senior and does not respect him as a person, but in crisis situations, they show excellent coordination by combining their abilities, and Zed acknowledges Zapp's genius. Zapp also utilizes Zed's abilities in battle. He is an adult.