This is the most correct way to sit in modern Japan. It can be said that it is a very basic method used in martial arts such as kendo and judo, arts such as tea ceremony and flower arrangement, and also in ritual places such as Shinto and Buddhist affairs.
However, it is surprising that it was after the Meiji Era that the name “Seiza” was given and it was made an official way of sitting. The sitting itself has probably been done for a long time. But it wasn’t until the beginning of the Edo period when it became widely recognized as a formal way to sit down.
Originally, Japan is a kimono culture. It seems that it this way of sitting best suited the clothing worn in Japanese culture. There are many types and shapes of kimonos. Naturally, they greatly affect the way you sit. It’s really hard to avoid ruining the structure of the kimono, and to make sure that the work of dressing remains in shape. For that reason, kimono seems to have been devised in various ways to suit the proper form of sitting. At last, is that why this way of sitting, now called “proper sitting”, was developed…? There seems to be a sweeping generalization, but it probably does have some basis in truth.
Speaking of sitting, we’d also like to address numbness. Sit back as much as possible, do not loosen your abdominal muscles, make the left and right legs in the shape of an eight (it’s Japanese kanji “八”) and put the buttocks between the legs, and so on… There are various ways to prevent numbness… The best way is do not overdo it… It seems that you will feel numbness however you sit, but if you don’t get used to it, it will take a lot of strain on your feet. Perhaps sometimes decline sitting in seiza, get used to it gently, and it will feel much better.
By the way, there are many trends of sitting in seiza. To maintain the work of the kimono is not lost and remains beautiful. Based on these conditions, different methods are devised. Please check it out if you are interested.