The middle grandson, Sa Sakujun finds the world very boring and seeks to amuse himself without regard for morals. To relieve his boredom, who at the mere age of 15 Sakujun was the one who used and manipulated the Satsujinzoku as he pleased. Fourteen years ago, he found and recognized the young prince Seien (later Seiran) collapsed in the snow. Thinking it was well suited for him, he brought the young prince to the Satsujinzoku. Sakujun then covertly retaliated by killing Enjun's son and daughter-in-law in order to get back at him from the many bad experience he had years before.

When his grandfather Chusho tells him to marry the Kou princess, Sakujun assumes an alias as Lin Senya, a merchant's son, and arranges to meet Shuurei in person. He was neither interested in power nor being a leader but once he has his eyes set on something, by whatever means neccessary he will do everything to get it (Shuurei). In order to do so, he needed to get his older brother killed, Sōjun. This places Sakujun as the next in succession to become the Sa clan head, giving him more power to resist the Kou clan if he marries Shuurei against their wishes.

With his typical devious perversity, he eventually allows Shuurei to poison him without her knowledge. He is later assumed to be dead, although his body is never found. In the second series, he makes a dreamlike appearance to Eigetsu and frees him (presumably as a spirit). He is portrayed by Takehito Koyasu in the anime series.

Sakujun is now presummed to be the current host for the Black Immortal. When he lies under the tree under which Shuurei leaves him, Sakujun hears a voice in his head telling him that he finds him very interesting. Throughout the later parts of the novels, Sakujun becomes more active as he appears in various instances in the various temples for the Immortals in the Seven Clans of Colors and destroys many of them for a reason still to be revealed.