It may appear "weird" to some but it's a centuries long practiced, customary part of Japanese culture that's associated with the Samurai (See here). The Samurai were held in high regard in Japan and thus all of Japanese society had started to emulate the practice. Now there's a PC video game about it. That's all.

Other countries around the World may also have customs and practices that may appear "weird" to others (I could cite examples but I think that you understand my point). The enlightened thing to do is not to ridicule others for their differences and instead to try to learn to appreciate the differences (eg. - In the US, it is customary to drink beer ice cold. In England, it is customary to drink beer "warm" (See here).
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