In order to enter Japan, you need to go through the motions of the visit Japan website. You will need to either have a boosted vaccination record or a pre departure PCR test.

You will need to leave the airport due the overnight layover, so I doubt that they will let you through transit security so you can access the lounge. You would need a same day departure for that, which you don't have.
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There used to be a priority security lane, it was closed for a long while, since traffic was quite low. I don't know if it has reopened yet. There is no immigration fast track when leaving Japan again.
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