Assuming your seperate tickets have origin and destination points both from NRT or HND, then you could likely get one ticket changed to match the other so you can make the transit airside either at NRT or HND, regardless of separate tickets or same ticket. (Japan is very unlikely opening the borders anytime remotely soon, sadly). But, even via countries that do require a visa and you couldn't enter, still separate ticket transit is typically allowed if you don't check luggage or if your carrier allows through checked luggage on other carriers (separate ticket).
The other part of your initial question, "Landing" means entering the country in immigration terms. You never "land" if you never enter the country.
Last edited by dvs7310; May 11, 2020 at 11:49 am