Yuki Makimura

Yuki Makimura was a Slayer. She is notable as the only known Slayer who was turned into a vampire. Because of this, the Watchers' Council omitted her from their records.

Although her original appearances are non-canon, Yuki herself is a canonical character since she cameos in Tales of the Slayers.

Biography
Yuki Makimura was called as a Slayer in Japan. She is trained by a samurai Watcher. Yuki's Watcher fails in his duty, and in penance, commits Seppuku. Three months after his death, Yuki goes up against the Master, who kills and sires her. While most Slayers welcome death, Yuki didn't want to die. Upon becoming a vampire, Yuki gives her complete loyalty to the Master and serves him willingly from Japan. The Watchers' Council removed Yuki from their records, but failed to cover up the two missing years in the Slayer timeline.

Dawn discovers Yuki's missing time slot and Spike tells of the disgraced Slayer-turned-vampire. Yuki comes to Sunnydale with her blind vampire henchmen to resurrect her sire in either late 2000 or early 2001. She plans to get revenge on Spike for killing the Anointed One and to use Xander as a vessel for resurrecting the Master. Dawn stops the Master's resurrection and Yuki is staked.