Originally Posted by
CPH-Flyer
The Japanese rules clearly says "transit to a 3rd county" is allowed. There are a few exceptions that works just fine, most notably mainland US to Guam via Japan. But I would imagine SQ to be quite by the book, so no leniency on the rules and you'd be stopped in Singapore.
B2B flights are doable in many places these days, just currently not in Japan.
Would a BKK-NRT via JL and NRT-SIN via SQ (check-in online) on 2 separate bookings be workable? Just called SQ, and being very "by the book", they said that if the SQ boarding pass destination shows NRT, I must clear immigration. (?)