Originally Posted by MSPeconomist

You could do two of BKK, HKG and SIN open jaw and purchase cheap tickets to Vietnam and elsewhere in Thailand. SIN is reputed to have some good cheap airlines/fares. BKK too, but the quality might be worse; some of their LCCs sound pretty bad to me, but no personal experience. From HKG, I'm not sure what the situation is.

I would suggest skipping Japan because you risk trying to do too much, but you might be able to route inbound through HNL and arrive late enough in the day that you have a close to 24 hour overnight connection at NRT to elsewhere in Asia, although remember that NRT is far from downtown Tokyo. Alternatively, you could route into HND, arrive close to midnight, and then enjoy a bit of Tokyo nightlife and part of the following day before heading to NRT for your intraAsia connection. If you're energetic, you could even avoid taking a hotel by storing your bags, doing bars until very late, and then heading directly for the fish market to see the action before dawn. Have sushi for breakfast in a stall there and then think about the tourist stuff you want to do before going to the airport.

Note: Anything less than 24 hours on international counts as a connection, not a stopover, and at NRT (unlike SIN, BKK, and HKG now that DTW-HKG and vv is gone) you can use this to your advantage. You just need to find DL flights that arrive into NRT or HND later than the DL's late afternoon connections to elsewhere in Asia, so that you must spend the night in Tokyo and catch the next day's connection.

Also: There might be a limit of four flights in each direction (three connections) on your ticket. You need to look at the specific L class fare rules for different fare codes that are L class.