Master Sensei

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Master Sensei is the head teacher of the Yamanouchi Ninja School. He has many different skills and he has mastered Levitation and Astral Projection.

He has instructed many ninja students:
 * Yori, who befriended Ron Stoppable.
 * Hirotaka, who was attending Middleton High School for a week during the whole student exchange program.
 * Fukushima, who betrayed the school and allied himself with Monkey Fist. He was defeated by Ron Stoppable, who managed to channel his Mystical Monkey Power for the first time.
 * Ron Stoppable, who was the Middleton High School Student, who was sent to spend a week learning at the Yamanouchi Ninja School, which was arranged by Master Sensei. He pretty much has failed every class at the school, even though he is connected to both the school and the Lotus Blade by destiny, due to his Mystical Monkey Powers
 * Rufus, who attended each class, along with Ron Stoppable, only he excelled at almost everything, unlike his owner, Ron.

Master Sensei also knew that both Monkey Fist and Ron Stoppable were exposed to Mystical Monkey Powers. He was also aware that Ron had some deep-rooted monkey issues, as well as Ron being the anoited prophesized Ultimate Monkey Master. That is problably the major reason why he arranged for the two schools to do the Exchange Program for a week. It was very important that he met Ron Stopable, and to help prepare him some for his destiny of being the Ultimate Monkey Master. Like Yori, he really believes in Ron.

In the episode "Big Brother", Master Sensei secretly arranged for Mr. Stoppable and Mrs. Stoppable to adopt Hana Stoppable, who knew that she was the prophesized Mystical Weapon, because he knew that it was imperative in both, Ron and Hana's Destinies that they be brother and sister. He chose to place Hana with the Stoppable Family, when Monkey Fist was searching for the mystical keys concerning the Mystical Weapon, who was Hana Stoppable. He knew that Ron needed to prepare her for her upcoming battle against the Yono the Destroyer. He did not tell this to Ron, though. He waited until Ron and Kim Possible, both saw Baby Hana walking on the ceiling, and begin trying to find out about Hana's adoption agency, which of course led them back to Master Sensei and the Yamanouchi Ninja School. He broke this information to Ron, in much the same way as Ron's own parents break major news to him, "This is my way of telling you." Thankfully, Ron teaching Hana to turn the "page," and to dance to the Flippies helped her to win and defeat Monkey Fist and the Yono. In the battle against Yono the Destroyer, he was the second one turned into stone (Rufus was first, and Kim was third).