>>1715017LCC airlines fly NRT-KIX I believe. You're right about the slot restrictions for HND/ITM. Haneda has been at 100% capacity for as long as I can remember, maybe even longer than Heathrow. Meanwhile, Narita has been expanding and expanding, on both the passenger and freight side.
Freight: Haneda and Itami are heavily slot restricted and don't have space for cargo flights, which have to use Narita or Kansai. FedEx, DHL and Yamato Transport have big hubs at Narita, and NRT-ANC is a busy freight route.
Passenger: The goal was to soak up the demand for LCC and tier-2 Chinese cities as well as tourist demand for the 2020 Games. Terminal 3, shortened curfew (at Kobe Airport/UKB as well), even a new third runway.
...at least, that WAS the plan, until COVID fucked everything up.
In a post COVID world, I wonder how Narita and Haneda's roles will grow or diminish. I personally think Narita will continue to grow, since it's the only choice for cargo flights, and is a hub for LCC routes across Asia. Demand for tier 2 Chinese cities will also rebound eventually. Japan and China are in a mutually dependent economic relationship.
I also think Haneda will have steady growth, but driven by the international side. Japan's population continues to contract which lowers demand for domestic air travel. And LCC routes out of Narita are cannibalizing Haneda's domestic market. But Haneda will remain a prime O&D destination from the USA and western Europe, South Asia and Aus/NZ, particularly the financial hubs of Singapore, Hong Kong, KL and Sydney.
Interestingly, JAL, ANA and a couple of other airlines had planned a huge shift from Narita to Haneda in March 2020, following Delta's move to Haneda. This had to be scrapped due to the pandemic. Some of the flights I remember:
JL749/740 NRT-DEL replaced with
JL39/30 HND-DEL
AI306/307 DEL-NRT switching to HND
TK52/53 IST-NRT replaced with
TK198/199 IST-HND
