Tan Kai, also known as Dan Hai, is a key assistant to Emperor Xia Gaojun, primarily gathering intelligence and acting as the emperor's eyes and ears beyond the inner palace. Despite his generally laid-back demeanor, he performs these duties competently. He originated as the son of a noble family that lost their fortune. This downfall forced him into banditry for survival. Following his arrest, he was condemned to castration, becoming a eunuch. Assigned to serve within the inner palace after this punishment, his responsibilities later shifted towards protection. He became one of Liu Shouxue's bodyguards after an incident involving Xiaoyue, balancing this with his intelligence work. His anime debut occurs earlier than in the original light novels, specifically within the Flower Whistle chapter adaptation from Volume 1, contrasting with his first novel appearance in Volume 3.