Originally Posted by
erik123
Most cheap fares don't allow stopovers. I suggest you experiment with google flights. Also look at an open jaw flying into Japan and out of Seoul - buying the one way from japan to Korea separately. If you fly through Through you can likely add that to the mix (eg in AMS on KLM).
IME, airlines that are stated owned (even partially), or have other reasons to support the economy in their base cities, often have fairly generous stopover rules at their hubs. For example, MU, CA, JL, CI, and CX come to mind.