Yoru Sensei was Bruce Wayne's martial artist teacher in Batman: The Animated Series.
History[]
Yoru was the master of martial arts academy in Japan where Bruce enrolled in. He trained himself extensively in martial arts and became one of the best students at the dojo, aside from Kyodai Ken who consistently beat him. Bruce kept practicing intensely to improve his skills, partially out of concern about being able to keep operating as Batman, during which Yoru told Bruce that he could learn much from defeat rather than victory. Ultimately, his lessons helped Bruce shape up into becoming Batman due to taking this lesson to heart as he matured. When Yoru saw Kyodai stealing a sword from the dojo, he expelled him from the academy.
Years later, Kyodai Ken returned to Japan and kidnapped Yoru's prized pupil Kairi Tanaga as a bargaining chip for an ancient secret. Yoru called Bruce to tell him that he needs Batman's help, implying that he knows his student's secret. Along the way, Bruce learned that Yoru was the last direct descendant of a sensei who invented a deadly fighting art known as The Way of the Fang, a style of fighting that was technically discontinued by that same sensei long ago due to how dangerous it was. However, it was still transcribed on scrolls, with said scrolls being hidden in a cave and the location only being known to the family patriarch so it could be passed down from one generation to the next. Yoru never sought or made any use of it due to being afraid of what he could do with it, but this created a problem in the present since Kyodai was demanding that he give the scroll to him in exchange for ensuring Kairi's safety. Bruce initially suggested that Yoru should give him a false map so that he wouldn't be able to find it and give up, but he didn't agree to this due to being devoted to the concept of Bushido, which encourages samurai to be honest and honorable even in scenarios like the one they were in, and didn't want to risk Kairi's life since she would be in grave danger if Kyodai caught on to the deception. Therefore, they managed to track down the real map and the scroll to bring to Kyodai.
Later on, after Bruce had confronted and fought Kyodai on Mount Kajiiki, during which Kyodai died as a result of a lava explosion, Yoru took the opportunity to ask him to thank Batman on his behalf before he left Japan. Bruce felt ashamed upon being given this request due to thinking that Batman (in other words, himself) wasn't deserving of such thanks due to relying on tactics like darkness and fear, making him no better than Kyodai, but Yoru disagreed and reassured him that Batman actually showcased many of the traditional values that the samurai prioritize like resolve, honor and showing mercy even towards enemies.