Similar to what CPH-Flyer said above, the fare classes eligible for upgrade using non-ANA miles is quite limited. Those are the highest group of fare classes and unlikely to be what you're considering if looking for a cheap fare. I don't know your departure city, but just did a search round trip from ORD-TYO next year on random dates. A "U" fare is over $2,000 more expensive than a "K" fare (NH's cheapest economy fare).

You'd be better off looking at the Premium Fares forum, there are some good Premium Economy or Business fares on NH to SE Asia from time to time and you can add a stopover in Tokyo in one direction for minimal cost. Recently those have all been out of NYC, but LAX pops up sometimes too.

Just for reference, here's what you can upgrade on NH metal using United instruments:

Using Star Alliance upgrade on Economy ticket:
https://www.united.com/ual/en/us/fly...de-awards.html
Booking classes: Y, B, Plus J, Z, E, G, M and U

Using UA Plus Points
https://www.united.com/ual/en/us/fly...Lufthansa.html
Booking classes eligible: B, C, D, E, G, J, M, U and Y.