Billy is one of the Four Heavenly Kings and a self-proclaimed genius. He's actually very smart in science and mathematics, but is otherwise stupid and not very competent in his work.
He temporarily becomes a student at St. Cherine Academy's middle school under the alias Shouri Tanaka, in order to uncover the identities of Angel Rose and Angel Sapphire. After failing to identify them, he is kicked out of the Four Heavenly Kings by Mary, but later returns to take revenge on her.