Zephel is a 17-year-old male commoner from an industrial planetoid belt, born on June 4 under the Gemini sign with blood type B. He stands approximately 169-171 cm tall, weighs 51-53 kg, and has platinum hair with eyes that are ruby red or aubergine in color. Both of his parents are present; his father worked as a factory engineer. Zephel balances rebellious tendencies with an underlying gentleness and possesses a strong interest in machinery and technology. His hobbies include tinkering with machines, playing squash, and rollerblading, with specific interests in nanomachines and environmental topics. He favors chicken curry, tacos, and mineral water, but dislikes jam, fresh cream, fruit in salads, and candy. His favorite scents include soap, he values mechanical engineering books, and his favorite animal is the cat. Socially, he considers Luva his best friend and Randy his worst friend, describing his ideal romantic partner as "an average girl."

As the Guardian of Steel, Zephel represents the "Sacrea" of technology and ingenuity related to processing metals and minerals. He became a messenger from the Sanctuary at age 16 and assumed his Guardian role that same year. Initially reluctant to participate in formal duties—such as avoiding interviews during the Legendary Etoile selection—he later demonstrates responsibility by assisting the protagonist Ange in her mission to restore balance across universes. This includes chastising Ange for not seeking help and participating in efforts to release Sacrea energy to revitalize struggling worlds. His narrative in the second season involves confronting the difficult fate of Guardians, who are forcibly separated from their families at young ages due to their powers and face isolation as time passes differently in the Holy Land compared to their homelands.