The middle brother. He finds the world very boring and seeks to amuse himself; morals are of no consequence. Upon being told by his grandfather that he is to marry the Kō princess, Sakujun arranges to meet Shūrei in person, under the disguised name of Lin Senya, and finds himself intrigued by her (though Shūrei was twelve years his junior and he was old enough to be her uncle).
It is later revealed that Sakujun supports the Satsujinzoku, having been with them since a teenager to relieve his boredom. Fourteen years ago, he finds Seiran collapsed in the snow and takes him into the band, already knowing of Seiran's past. Nine years ago, in retaliation for all the obstacles his great-granduncle, Sa Enjun, places in his way in hopes of reining him in, Sakujun kills his uncle and aunt, the son and daughter-in-law of Enjun, as they were within his reach as Enjun was not.
Desiring Shūrei and yet understanding the power of the Kō Clan, Sakujun arranges the murder of his elder brother, Sōjun, so that he may become head of the Sa family instead. This is in order to have the power of the clan to wield against the Kō should they protest his taking Shūrei to be his wife.
He is later assumed to be dead, after consuming a poison he intentionally drank. However, his body is no where to be found and in the second series, he made a dreamlike appearance to one of the characters (presumably as a spirit).