Uranium-238. A girl. She has a quiet and reserved personality. She has a green bob haircut and yellow eyes. She wears the same sailor uniform as Uranium-235. She is protected by fuel rods. When hit by fast neutrons, she cannot withstand the energy and undergoes fission "rarely." Incidentally, if she captures a thermal neutron and can endure the massive energy, she becomes Plutonium and her personality changes. She also plays a role in stabilizing the inside of the reactor by absorbing neutrons. She rarely undergoes fission in light-water reactors.

Uranium-235. A girl. She is energetic and full of energy. She has short bangs above her eyebrows and a wolf cut. Her hair is light green and her eyes are light yellow. She wears the same sailor uniform as Uranium-238. She is protected by fuel rods. When she captures a thermal neutron, she cannot endure it, undergoes fission, and becomes a different person. Since she becomes a substance often called "death ash," she has accepted the fate of being essentially disposable.

Thermal Neutron. A girl. She is energetic but a bit eerie. Since the original substance (a neutron) can only live as a thermal neutron for 15 minutes, she has a clingy, unstable "menhera" streak. Desperate to be captured, she loves moving around and flies through the air. Her bangs are a bit long, covering her eyes. Her hair is collarbone-length in half-twin tails. Her hair is orange and her eyes are light blue. Atomic-related objects orbit her head. She wears a long-sleeved T-shirt. She floats weightlessly in the air.

Fast Neutron. A girl. She is young in both appearance and personality, a neutron with high velocity. She flies around frequently. Her bangs are above her eyes. Her hair is mouth-length in half-twin tails. Her hair is orange and her eyes are light blue. Atomic-related objects orbit her head. She wears a long, one-piece dress with a rounded collar. A neutron's goal is to be captured, but newborn fast neutrons are often too fast for substances to catch. Therefore, in a reactor, they grow into thermal neutrons via a moderator. She floats weightlessly in the air.

Water. A woman. The ultimate mother figure. She possesses incredible maternal tolerance. Her bangs are above her eyes, side hair is below the jaw, and back hair reaches below her chest in braided twin tails tied with red cords. Her hair is blue. She always keeps her eyes closed, and no one has ever seen their color. She can see her surroundings even with her eyes closed. She wears a bandana on her head and a shirt with an apron. She educates (slows down) fast neutrons and cools the fuel rods and the Uraniums.