The Four Schools (四流派,Yon-ryūha?), are schools created by Fudo Myo-o.
Each school have a license that can be downloaded by a Samurai's key.
Licenses together with Locker Balls are essentialy devices to run a program that controls the Binding and Spliting of matter. Each school has a special skill that their members can use, however these can be used by other Samurai if a Key is connected to the other Samurai’s Key, as seen with Benkei.