Kokujun Sa belongs to the Sa Clan, one of Saiunkoku's eight noble families, known as the Brown Clan. He is the youngest grandson of Sa Chuushou and son of Sa Bou, with two older brothers, Sa Soujun and Sa Sakujun. Eighteen years old at the series' start, he displays notable kindness. This gentle nature leads others in his clan to perceive him as the weakest of Chuushou's descendants. His demeanor reminds Lady Hyou Eiki and Sa Sakujun of a younger Sa Enjun, the former Sa Clan head and one of the Emperor's Grand Advisors. Kokujun harbors deep affection for his cousin, Sa Shunki, granddaughter of Sa Enjun and Hyou Eiki. When Shunki faces danger within clan power struggles, Kokujun intervenes. He releases Shi Seiran and Ro Ensei from confinement to rescue her. Ensei harshly rebukes Kokujun for his passivity, challenging him to take direct action. This confrontation acts as a catalyst. Kokujun personally escorts To Eigetsu and Kourin (posing as Kou Shuurei) to Kinka, deliberately concealing his awareness of Kourin's identity. This act demonstrates his initial steps toward assertiveness. Following the Sa clan leadership ring's recovery, Kokujun ascends to clan head with Shunki's support. His leadership marks a transformation from his earlier perceived weakness. He solidifies his authority by formally pledging loyalty to Emperor Ryuuki during the New Year ceremonies, publicly debuting as the Sa Clan's legitimate leader. Kokujun maintains a close friendship with Ran Ryuuren of the Ran Clan (Indigo Clan). The same age, Kokujun holds deep admiration for Ryuuren, whose eccentric and independent nature may have indirectly influenced Kokujun's journey toward self-assurance. His marriage to Shunki further stabilizes his position and connects him to the Hyou Clan's heritage through her lineage. His character arc progresses from a gentle, underestimated figure to a committed leader prioritizing clan stability and honor. This development is rooted in his foundational kindness, which evolves into a strength as he learns to balance compassion with decisive action.