Here is what happened: my friend came to Osaka, entering Japan on a single-entry tourist visa for 90 days. We decided to go to Indonesia, both of us entered with a visa on arrival, stayed there for few days, and returned to Osaka.
But, when we arrived in Osaka, my friend was denied entry, even though he's still within the 90 days his visa is valid.
He has to return to his home country and I have paid for the ticket, using the same airline which we both flew from Indonesia to Osaka.
In this case, who is responsible for paying the airfare to return to his home country?
I agree it is my friend's responsibility to check the visa type, but the airline should not have let him board the flight to Osaka from Indonesia.