Airlines refusing check-in without return ticket

It's true, with the proviso that this rule doesn't apply to people who are already entitled to live in Japan. For instance, last time I flew to Japan one way, I had to show my Japanese residency visa before they'd let me board. I've heard stories of people being forced to buy onward tickets from Japan to Korea at the airport.

One trick I've heard of to get around this problem is to go on-line and buy a ferry ticket from Hakata, Japan to Busan, South Korea before you travel. Once you arrive in Japan, you can cancel the ticket and get most of the money refunded. I can't vouch for this method myself, but other people claim to have used it.

But, of course, that still leaves you with the problem of being in Japan with neither a residency visa nor a ticket out of there. Overstaying your visa is not recommended.

Not an urban legend - my friend tried to travel from Glasgow airport on a one-way ticket and was forced to buy a one-way ticket to anywhere out of the country at the airport (he chose South Korea) before he was allowed to check in.

Of course if you have a valid visa / special re-entry permission then you'll be fine.

Regarding other countries: I also had to prove I had onward travel from Vietnam before I could board the outbound plane.

Being allowed to enter, depends on the Airlines, and migration officials in both countries. I took a ferry from S. Korea to Japan and back again. When I tried to leave Japan, migration didn't want to let me on the ferry because I didn't have other tickets. I had to explain I had a Korean work visa. In Fiji, Korean Air didn't want to let me board the plane because I didn't have on proof of further travel, and I had to explain to them about my visa. Being a middle-aged U.S. female, they tended to believe me. IF you are an E.U. citizen, and can tell them about further travel plans you should be able to enter Japan.

Hint: There is a ferry that goes from Fukuoka to Busan S. Korea, but make sure to hide your tatoos going through Japanese immigration.

With British Airways I had to prove onward travel from Israel (USA Passport), which I did by purchasing on the spot a return one-way refundable ticket that I had refunded on arrival in Israel. British hit upon the profitable idea of selling it to me in GB Pounds and refunding the same quantity but in US Dollars; it took a few weeks but the credit card company fixed it.

At the same time I was flying into Israel on TWA (RIP), Air France, and Air Canada, and a small Israeli charter airline, none of which enforced a return ticket requirement.

As the various examples people have given show this really does happen.

What's going on here is that the airlines are subject to substantial fines if they bring in a passenger which is obviously inadmissible. Thus if a country requires a ticket for onward travel the airlines are very likely to ask to see this ticket before boarding you.

You'll find the same thing with visas--they check your passport and visa before allowing you to board. Usually this is a good thing, getting tossed out as inadmissible isn't a good thing. Unfortunately, it sometimes involves airline employees who either think they know the rules and won't check (China always needs a visa....but these days you can do a transit without visa, in some cases for 3 days (edit: since I wrote that it's now 6 days in some situations) on the ground) or they don't understand the TIMATIC printout (it's written in legalese) or even when TIMATIC doesn't make it clear exactly how the rules work (That Chinese transit without visa must be a transit--you must leave to a different country than you came from. However, they only look at the airplanes, not the whole itinerary--a flight that goes A -> B -> China -> A qualifies. Enter the whole flight into TIMATIC and it says you need a visa. Enter only the two flight segments and it correctly permits the transit.)

(I'm not picking on China as a weird case, it's just one I've been in many times and thus pay attention to the rules.)