The concept of uchi and soto is a fundamental idea of Japanese social culture, which defines the distinction between us (uchi,内, "inside") and them (soto, 外, "outside"). Uchi and soto is what divides people into in-groups and out-groups and this idea is embedded in the culture so deeply that byproducts of the idea has shown in the Japanese language. For example, Japanese honorific language ("keigo") uses specific words and prefixes to show politeness, humbleness and respectful. Nouns involving the family, the household, or familial relations normally take honorific prefixes when denoting an out-group and not when denoting an in-group. By using honorific language to out-groups, it creates a barrier between them and in-groups, which reinforces the separation of those two groups.
                                                

Although this concept has been used as a great tool to mold the nation and bodies to be seen as polite and humble, it also can create uncomfortableness and wariness toward out-groups. Yumi Nakata points out “Foreigners, tourists and customers are always considered “soto” in Japanese society. Many visitors to Japan are generally impressed with the level of customer service, as Japanese people are generally polite to soto people, but it does not mean that their politeness and friendliness are sincere and they are genuinely trying to be your friend. Some of them may be truly interested in getting to know you but most of them are simply following the custom.” An intention to make bodies aware and be alerted to out-groups goes back to Robertson’s piece about eugenics in Japan.

Furthermore, uchi and soto did not only affect the social culture but also the hygiene culture. This idea plays a big role to define cleanliness and dirtiness. The Soul of a Nation: Japan’s Destiny emphasizes sanitary standards are largely rooted in their concepts of uchi and soto, that is inside and outside, because that which is inside is considered clean and whereas that which is outside is considered dirty. The author mentioned that Uchi actually means the house and what is not part of house, the outside world, is thought to be not clean. (Matsumoto,2009) This argument has a deep relation with hygiene as well. By separating spaces between clean inside and dirty outside world, Japanese bodies are rescued from the danger of contagion and feel relieved by being in safe space that allows the most privacy than any other spaces. Therefore, creating barriers between bodies was desirable to the nation because it prevents people from getting infected due to unwanted contacts with human feces, which goes back to the physical health component.

It is riveting to see the deep connection between these consequences of uchi and soto: social distance and physical distance. This connection goes back to Foucault's and Mauss’ ideas of biopower and the importance of bodies. It is vague to spot which one social or physical distance was a starting point of uchi and soto. However, it is clear that each has been influenced one another and created the unique culture of Japan. This uniqueness has reinforced and reinterpreted  by the nation, the society and the bodies in Japan over time, which created the endless chain of power. (more details in page 5)

References
 

Foucault, M. (1990). The history of sexuality: The use of pleasure (Vol. 2). Vintage.
Mauss, M. (1973). Techniques of the body∗. Economy and society, 2(1), 70-88.
Matsumoto, D. (2009). The Soul of a Nation: Japan's Destiny. Morgan James Publishing.
Nakata, Y. (n.d.). Uchi Soto and Japanese Group Culture. Retrieved April 23, 2017, from https://blog.gaijinpot.com/uchi-soto-japanese-culture/