If you are thinking 'bout the cruise line in the states, please check "Princess Cruise Line". I heard they have a guest desk for Japanese passengers on board.
As far as I know, some of these cruise lines usually hire people for the HQ office job first. After you work in the office (such as a reservation agent) for several months, you can apply for the jobs on board. It is because they want their stuff to know about the company very well before they send people on board.
As "A & B"-san mentioned, the pay is not that good. You will work your ass off. (LOL) But the experience is awesome and will learn a lot.
If I am not married, I would go for the position, too...
Oh, and if you have some special skills other than languages, you can apply for many different positions such as entertaining programs or child care programs or even doctor office on board.
There may be more options you can find, and it is not impossible.
Please keep trying to reach your dream. =)
Good Luck!