Sei Kyou, historically Cheng Jiao, served as the second crown prince of Qin and was the younger half-brother of King Ei Sei. He established the Sei Kyou Faction to advance his claim to the throne and purge non-noble bureaucrats from the Qin court. This faction initially allied with the Ketsu Shi Faction to orchestrate a rebellion against Ei Sei, aiming to overthrow him. The coup, known as the Sei Kyou Rebellion, failed. Following this defeat, authorities imprisoned Sei Kyou, and his faction largely withdrew from court politics. Ei Sei eventually ordered Sei Kyou's release. Once free, Sei Kyou agreed to support his half-brother against their common rival, Ryo Fui, refusing to accept a merchant like Ryo Fui holding political power in Qin. He then leveraged his connections to bolster Ei Sei's faction, significantly increasing its influence within the court. His actions during this period demonstrated a shift toward prioritizing Qin's stability, working for the nation's interests despite their past conflict. Ei Sei later appointed Sei Kyou as his regent, granting him absolute political control over the royal court during the king's absence. Sei Kyou was ultimately slain by rebel soldiers. After his death, leadership of the Sei Kyou Faction passed to his first wife, Rui, who continued aligning the faction with Ei Sei's rule. Prominent faction members included his teacher Ju Haku, killed during the rebellion, and strategist Shi Shi, who later defected to Ei Sei's faction.