Billy's one of the Four Heavenly Kings and never lets anyone forget he's a genius—though he's only actually brilliant when it comes to science and math. Everything else? Not so much. His competence outside those subjects is pretty questionable, to be honest.
He went undercover at St. Cherine Academy's middle school for a while, posing as a student named Shouri Tanaka. His mission was to figure out who Angel Rose and Angel Sapphire really were, but he struck out. That failure got him kicked out of the Four Heavenly Kings by Mary, which obviously didn't sit well with him. He's since made his way back, though—and he's got revenge on his mind.
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