Japanese martial arts, such as Sumo, Karate, Judo, Kendo, Aikido are the intriguing aspect of Japanese culture. It all are invented to battle with enemies as well as train the inner self and cultivate respect and courtesy to your enemy, so that rough barbaric worrier can be disciplined into a SAMURAI who serves to their master. It makes the Japanese martial arts even more attractive and adds the depth of it.
You can visit the training site of these or even try them, if you like peeping into the depth of it.