I haven't bought anything yet. First trying to understand the least expensive ways I can have advance seat selection on JL metal.

So here is the scenario. USA-SE Asia ticket:

USA - Tokyo (prefer AA in order to use SWU)
Tokyo - SE Asia (JL metal, can be AA or JL coded, whichever lets me have pre-reserved seat)
SE Asia - Tokyo (JL metal, can be AA or JL coded, whichever lets me have pre-reserved seat)
Tokyo - USA (prefer AA in order to use SWU)

I am trying to understand what the marketing carrier and booking code should be between SE Asia and Tokyo so I can have pre-reserved seating.