Originally Posted by
SkyTeam777
Im arriving from FRA on my way to ICN. Do I have to leave customs to go here and then re-enter?
Correct. It's doable, albeit somewhat rushed.
Arrive >>> Immigration >>> Customs >>> Spa >> Security >>> Immigration >>> Lounge >>> Boarding
If the immigration line to enter Japan takes more than 30 minutes, give up and do an airside transfer to your next flight (That will mean a security check, but no immigration and customs).