This way of sitting is called “seiza” in Japan. This style of sitting is required for traditional Japanese events and formal ceremonies today. In fact, samurai and ninja generally did not sit this way long time ago. Because seiza does not allow you to move quickly. It means that it takes time to move to standing and attacking movements. However, to put it the other way around, Seiza indicates that there is no intention to attack. Therefore, it is said that subordinates began “seiza” in front of the shogun and high-ranking samurai from someday. Today, it has become a common way of sitting in formal situations in Japan.
However, seiza is difficult if you are not used to it. If you come to Japan, you don't have to force yourself to do seiza. Don't worry, it's not rude if you can't do seiza.
