https://www.tokyo-np.co.jp/s/article...301001165.html
If there's anyone suspected of having the virus upon arrival is indeed found to have the virus, then no one on the flight is allowed entry to Jpn and everyone is routed to quarantine / holding pattern.
I'm not sure if this is going to be any different than what they've already been doing. I don't know if this is at all a significant change.