Koto Ryu Koppojutsu Happo Biken (Knocking Down Tiger School) is a ninjutsu school of unknown origin. It is believed that the techniques originated in China and were brought to Japan from Korea. It was later organised into a ryu by Sakagami Taro Kunishige in 1542. Sakagami was also soke of Gyokko Ryu Koshijutsu.
The speciality of the school are very strong attacks known as koppojutsu (bone breaking methods). There are also attacks at the opponent's eyes, nose and mouth. It also uses metsubushi (blinding or distraction methods).
Due to the bone breaking attacks, as well as the other attacks using fingers, the practitioners needed extremely strong fingers and toes. This strength was achieved by daily training plunging the finger and toes into sand or gravel. Masters of this art could rip the bark off trees with their bare hands.
The current soke is Masaaki Hatsumi.