I'm a Nepalese citizen traveling to Nepal from Japan and holding the Japanese resident card have 19hours layover in Icheon airport Seoul via Korean Airlines. Do I need a transit visa?
TIMATIC, the database used by airlines, states:
TWOV (Transit Without Visa): Visa required, except for Passengers transiting through Seoul (ICN) with a confirmed onward ticket for a flight to a third country within 24 hours. They must stay in the international transit area of the airport and have documents required for the next destination.
So if you stay in the transit area for 19 hours you don’t need a visa. That means you can’t leave the airport to go into the city, a hotel or to re-check your luggage.