The Yamanouchi Ninja School (山内忍者学校) is located in one of the Yamanouchis in Japan. It was founded by Toshimiru, who made the school in 338 A.D. He carved the school by using only The Lotus Blade, a mystical blade which will only change forms if it is wielded by one who has Mystical Monkey Power.
The major teacher of the Yamanouchi Ninja School is Master Sensei. This is also the school of various student.
- 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.
The school has the Lotus Blade somewhere on its grounds, except when Fukushima told Monkey Fist where it was, so that Monkey Fist could steal it.
Three different characters are connected to the school by destiny, because of their Mystical Monkey Powers:
Another character, referred to as a Mystical Secret Weapon, is also connected to this school by destiny. Her name is Hana Stoppable and she happens to be Ron's adopted sister from the episode "Big Bother" and afterward. Her adoption was arranged by Master Sensei, who knew that she was the prophesied Mystical Secret Weapon, and that it is essential that she become Ron Stoppable's sister.
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 anointed prophesied Ultimate Monkey Master.
- There are 10 Yamanouchi locations in Japan.