my experience

There is one aspect common to all interviews at Japanese affiliated companies abroad in case of decision making process. Final acceptance comes from Japanese manager superior to the local English, French, German etc. HR manager. Therefore, you still have a step to overcome and too much enthusiasm is not the right understanding of the situation you are in. It is no exception, that for more senior roles you would have to go through the interview with company president, of course Japanese one. On the other hand, if you are already that far, it is merely formal matter to offer you desired position in the company. Selection process itself may take one or two months, depending on how busy company managers are and usually it has about three to five rounds-interviews. So to sum up, first of all be patient and keep showing interest.