Travelling between Japan and South Korea

You can get a Hydrofoil between Fukuoka and Busan. It costs 13 000 yen per adult one way and takes about three hours. A few leave each day but you will need to book ahead. You book online and when you check in you'll need to show the credit card you used to pay for it, or some other proof of purchase. There is also a 1 500 yen 'fuel surcharge' payment when you check in. I took one three years ago and had no dramas. However I had to book months in advance as it was the holiday season.

You can also get a ferry from Shimonoseki to Busan. It's a bit cheaper, however it is about 10 hours and the website isn't in English.

Once in Busan you can get to Seoul by taking an 'Express Bus'. They are very cheap and run frequently. No pre-booking is required.

here is a transportation tip in Korea. If you are planing to visit Korea from Japan by ferry, and move to Seoul area from Busan, taking KTX(train) is better than taking a bus. You can save your time and KTX is the fastest way from Busan to Seoul. Seat is convenient and you can buy some food in the train. Also if you are with friends you can buy a save pass too. If you have this pass, you can take any KTX everywhere you want to. And there is express train between Seoul station and Incheon International Airport so if you are going to the airport, you can take this train. Thanks.