For over a decade I've entered Japan on one-way tickets and no airline has asked for my proof of return/onward flights, so I stopped obtaining them long ago.

However a few days ago I arrived at BKK airport and VietJet Air would not allow me to board my flight to Fukuoka without a ticket out of Japan!

This was my first flight with VietJet Air so I had no prior expectations. I arrived extremely early but there was an extremely long queue at the check in counter. I was chatting a to Chinese American guy in front of me in the queue who foreshadowed what was about to happen to me. He told me he booked with VietJet Air accidentally because he has a policy of never using them any more after one time they wouldn't let him board a flight without proof of onward travel and he had to buy a ticket on the spot, which he did not want to do as, like me, he likes to adapt his travel plans as he goes.

I thought he was overreacting and told him that all airlines will do this when the destination country charges makes them pay for passengers denied entry to due not having a return/onward flight, but that most airlines to my knowledge only do this depending on things since as the nationality of the passenger, etc. I told him I'd been asked for proof several times in Singapore and Malaysia but not elsewhere and definitely never for Japan.

Well I was wrong this time. But was he right in saying that VietJet Air are to blame for applying this rule in a blanket fashion to all passengers? Or is it actually random and I was just lucky never being checked on flights to Japan for over a decade? Or could this be a post-covid effect where things are still a bit stiff and complicated as everyone returns from strict travel regime to a more normal relaxed system?