to put some perspective on the off days.
All your commute travel must be done on your days off, so factor that in.
If you live a few time zones away from Japan, factor the continuous adjustment for the body clock, twice a month.
There have been issue in the past and still occur, where the last duty before days off mean you cannot leave for home until the first day off, so possibly scratch another day there.
The potential for 14 off in a row and the flexibility in how one uses on's days off is great here and is probably one of the main reasons so many of the guys stay here. It is not set in the contract and is something the company tries to assist with but can be taken away anytime it suits them