Sai Shou heads the Merchant's Guild branch in Kinka and serves as Prefectural Head within Sa Province. He strictly adheres to a core merchant principle of never fully committing his resources or abilities, always reserving a portion as a precaution, defining his cautious and calculating nature. However, he maintains personal morals that occasionally override purely profit-driven decisions. He has a twin sister, Sai Rin, who leads the Merchant's Guild in Koren Province, and their father is Sai Shin. During Shuurei's initial visit to the Merchant's Guild, Sai Shou escorted her to meet a man she mistakenly believed was the guild leader. Only after Shuurei secured the guild's support did he reveal the massacre of the Rin Clan, casting doubt on her companion's identity. Sai Shou formally introduced himself to Shuurei as the true Guild Head during her recovery, surprising her with his youthfulness in attaining the position. In negotiations, he pledged 80% of the Merchant Guild's resources to aid newly appointed governors, contingent upon restoring peace in Sa Province and dismantling the corrupt Sa Clan's power structure. Following the Sa Clan's selection ceremony, he deployed the guild's mercenaries to stabilize Koren. Sa Chuushou later commissioned him to forge a replacement Sa Clan ring. Sai Shou betrayed this request, refusing to deliver the near-perfect imitation he created, declaring that despite being a merchant, he still adhered to moral principles. He also facilitated the delivery of poison ordered by Seiran. After the Sa Clan incident concluded, Sai Shou experienced a significant shift in perspective. Recognizing a latent sense of civic duty within himself, described as "the blood of a government official," he resigned from the Merchant's Guild. He was last depicted studying alongside Ensei to pursue a career as a government official.