Lei Xiaoyu is a former operative of the Heilei assassin guild who now serves as a bodyguard for the Shinoyama clan. His primary assignment is to protect Sayo Shinoyama during her stay with the individual who is impersonating her half uncle, Polka Shinoyama. On the surface, Xiaoyu presents himself as capable, eager to please, and humble, but this pleasant demeanor conceals a deep-seated murderous intent. He regards the Polka impostor as an inherent threat to the Shinoyama family and also harbors a bitter grudge against the real Polka Shinoyama. This resentment stems from his intense filial admiration for Rozan Shinoyama, whom he views as a father figure, and a long-standing jealousy that Polka was the recipient of Rozan's fatherly affection. Over time, his jealousy has evolved into a superior complex: he believes himself to be the truly useful son to Rozan, more deserving of that role than the supposedly inferior Polka. Xiaoyu is extremely stubborn in his suspicions and convictions, often doubting or assuming the worst of the fake Polka even after Rozan expresses trust in the impostor. This stubbornness is fueled by his personal jealousies and his extreme devotion to the Shinoyamas, both of which drive his need to prove himself as the ideal bodyguard, servant, and surrogate son. He is proactive in pursuing his goals and intensely suspicious, sometimes to a comical degree, frequently engaging in eavesdropping and late-night activities. At the same time, his pride and self-confidence enable him to stand his ground against the Heilei and openly reject his blood family. As a former member of a skilled assassin organization, Xiaoyu possesses considerable combat ability, though his most defining traits remain his relentless suspicion, his conflicted loyalty, and his psychological struggle to earn the recognition he craves from Rozan.