Sei Kyou, also known as Cheng Jiao, served as the second prince of Qin and younger half-brother to King Ei Sei. Born to a Qin royal princess, his noble lineage was unquestioned. Initially consumed by resentment over Ei Sei's ascension, believing rulership required royal blood, Sei Kyou spearheaded a failed rebellion against the throne by allying with the Ketsu Shi Faction. This defeat led to three years of imprisonment. Following his release, Sei Kyou shifted allegiance, aiding Ei Sei against the powerful chancellor Ryo Fui. He recognized Ryo Fui's commoner origins as a greater threat to Qin's sovereignty than his own rivalry. During the Coalition Invasion, Ei Sei entrusted him with defending the capital, Kanyou. This act of trust proved pivotal, exposing Sei Kyou to Ei Sei's grand ambition to unify China and end perpetual warfare. Sei Kyou's personality underwent significant transformation. His youth displayed cruelty and cynicism, viewing humans as inherently selfish and manipulating others through his status. Post-imprisonment, he matured into a strategic and charismatic leader capable of inspiring fierce loyalty. His marriage to Rui, a princess from northeastern Qin, became central to his life, revealing a more humanized and compassionate side. He grew deeply devoted to her. His leadership was tested during the Conspiracy in the Court Arc. When Ryo Fui's faction attacked Tonryuu—where Rui resided—Sei Kyou rushed to its defense. Framed for treason by the traitorous general Ho Kaku, he faced imprisonment again. Demonstrating shrewd persuasion, he convinced his guards to release him by unraveling Ho Kaku's plot to eliminate witnesses and promising rewards from his treasury. Though severely injured fighting alongside his retainer Ju Haku (who perished), he prioritized Rui's safety. He ultimately killed Ho Kaku but succumbed to his wounds, dying in Rui's arms. His final words expressed regret at missing Ei Sei's unification and tasked Shin with protecting the king as both "sword and shield." Physically, Sei Kyou initially relied on subordinates like the enslaved warrior Ran Kai. Later, he displayed competent swordsmanship, holding his own against multiple foes despite injuries. Statistically, his leadership and intelligence were key strengths; his charisma ensured 90% of his faction remained loyal to Ei Sei after his death, far exceeding predictions. The faction, led by Rui afterward, continued supporting Ei Sei's reign. Philosophically, he began adhering to the belief in humanity's inherent corruption, contrasting Confucian ideals of innate goodness. This cynicism softened as he witnessed Ei Sei's vision. Historically, his character parallels the real Cheng Jiao, who rebelled against Qin Shi Huang (Ei Sei's counterpart) in 239 BCE and perished.