Outbound and return to/from Tokyo on different one way tickets. Issues?.
 

We have always visited Japan with RT tickets from the US. This time we are using miles on JL for inbound and UA for return back. I have heard that this can be a problem. As I will not have the BPs for the UA flights I will have the ticket numbers and receipts. Is that sufficient for a check in agent for JL to confirm we have return tickets and let us board?

On another note, my husband may have a business trip from HND out of the Japan, a few days after we arrive. He will come back 2 days later to rejoin us. If the meeting is cancelled and he just stays in Japan the whole time with us will immigration officials ask about this? I am sure I am overthinking this.

The requirement to enter Japan on a visa waiver is (amongst other things) that you have a flight out again. Since JL can't see it in their system being a UA ticket, they may ask to see the ticket. So bring a print of the E tickets, that is easier.

When you enter you are given a 90 days entry permit, apart from whether you intend to stay more than 90 days, no one will ask about your specific stay plans, and exit days.

I had separate tickets for SIN-NRT and NRT-SIN both on NH last year

At sin, NH agent asked to see return flight out of NRT , printout of PNR/itinerary was sufficient

When you enter Japan, you state your intended length of stay. This should match your return flight in case they ask to see it (which is rare). However, they grant you the maximum duration landing permission per your situation, which for US passport holders is 90 days, regardless of your stated intentions. At that point, you don't have to do anything if your plans change, as long as you don't exceed the 90 days. They don't keep track of what your originally-planned return flight is, and they grant you full permission to stay up to the 90 days.

Had 1-way award trips from LAX to NRT (and return NRT to LAX) on SQ...granted we were flying F and J but I don't even think they asked to see the return ticket when we checked in

As long as both are on SQ they can see it.

You'll be fine. I've done this loads of times. Just have a printout of your return/onward ticket for all passengers ready if asked. It's likely JL will ask at checkin; they are the only airline I fly that routinely asks if I have an onward ticket if not booked on the same reservation. It's unlikely that you will be asked for it at immigration but in principle they could.

When filling out the form at arrival, just put down your best guess for how long you will stay. It's ok if it changes later. They are mainly looking to confirm that it's < 90 days and matches any evidence of onward journey (if they even asked, which they likely won't).

No issue, flew to Japan in the winter from TPE on a one way award and had a separate return ticket also on an award back to the US. No one asked me anything in Japan.

Only EVA asked me about my return flight out of TPE when checking in to go from US to TPE. I told them I had a flight from TPE to KIX and they asked for proof.

We do this EVERY trip home (my wife is Japanese I am not) to Tokyo -- we always purchase one way tickets with cash / miles. In all the years we've done this I've been asked one time for when / how I was leaving... Just have your itinerary printed out and don't worry about it....

Japanese immigration has never asked me for proof of any onward journey (perhaps having a U.S. passport and not looking slovenly help). However, there have been plenty of flights to Japan where check-in has asked to see the outbound ticket.

Regardless, having two different one-ways won't matter, as long as you've got the proof.

I've done it several hundred times and have never once been asked either by the airline or at immigration to see a return ticket.

My tickets always terminate in Japan, I'd say it is 50/50 whether I am being asked if I have an onward ticket, or proof of residence.