you would pay VRT which is anything up to 30% (depends on emissions) of the value of the car. Thats the Open Market Selling Price of the car in Ireland, not the price you paid for it.
As for 'import tax' - don't know what you mean by that and as for VAT its not payable unless there is under 6000 km's on the clock. VAT is paid on a car once and once only, be that in the UK/Japan or where ever.