I am Pakistani national and was student in Japan. Now for further studies I am moving to the US. I have US student visa now. I am traveling from Japan and I have layover at Inchen Airport, Seoul for about 18 hours. Can I get the South Korean visa on arrival? It is long time for layover, I can't stay in transit area that long and I will like to go out.
You do not need a visa in order to transit Incheon airport, as long as your connection is less than 24 hours. However as a Pakistan citizen you will NOT be allowed exit the international transit area of the airport.
Your only option if you wish to exit the airport would be to obtain a tourist visa in advance. There are no options for obtaining one one arrival in South Korea.