Mike
I have moved the other way i.e. from Tokyo.
Key things to ask for:
-housing is about the same assuming you are at the mid to upper end. You will probably get better in Tokyo for the same.
-school fees can be steep - about JPY3m
-day to day living costs depend on what you eat and how you live but western good are not cheap e.g. bread, butter, cereals etc.
-cars are very cheap; stick to a japanese car
-petrol is about USD1.10 per litre
-taxis are very expensive, starting at JPY660 but the public transport system is very good and cheap
-air travel from Jpn is a bit expensive so see if you can annual travel allowance.
-expect to pay a monthly rent of JPY500,000 for a nice apartment of about 1500 sq feet in a cool area
-utility bills will be much much more than here. Allow for about USD750 per month as you will be running air con for about 4 months and heating for about 3-4 months.
Overall, if you can squeeze out a 25-30% cost of living differential, you will be living very well.
Also ask what your tax situation will be. Jpn taxes are slightly higher.
Feel free to PM me if you need any more info.
thanks