Tanaka Sensei was created by writers Chris Yost and Craig Kyle, along with artist Billy Tan. He first appeared in 2005's X-23: Innocence Lost #2.
Major Story Arcs
Tanaka worked for The Facility as a teacher for X-23. He was one of the very few people at the Facility who was kind to her. He called her "child" and told her that he was proud of her. This led to Dr. Zander Rice becoming upset with him. He instructed Tanaka that he was not to treat X-23 as a child and the only time he could touch her would be "to strike her down in combat." As an act of malice, Zander made him the final test for X-23's Trigger Scent. On X-23's "graduation day" he put a drop of the scent onto a sword that Tanaka was going to use. As soon as Tanaka grabbed the sword, X-23 reacted. Tanaka noticed something was wrong, but X-23 killed him before he could realize what was happening. His death affected X-23 greatly, even causing the otherwise emotionless girl to cry.
Afterwards, Zander had Tanaka's body burned and had X-23 punished by Kimura for breaking his rules by becoming close to Tanaka.