So basically the vast majority of Japan's cases are due to the colossal mismanagement of the quarantine on the ship.
A cruise ship is not an appropriate location for a quarantine -- it's a 3000 person cesspool. Many of the 500-odd passengers and crew who are now sick would not have been infected if everyone had been immediately sent to their home countries for quarantine on return, instead of being forced to wallow in improperly isolated rooms on the ship.
Also, you can't just quarantine for two weeks, you need to have a two week interval without any new infections. The two week counter should have been resetting every day that the "new infection count" wasn't zero.
Many of the passengers who tested negative are already infected, but they're going to send them home unencumbered anyway. This number is 50 times higher than it needed to be, and will cause this pandemic to fucking explode. I hope somebody goes to jail for this.