I searched around for a flashcard program (that was free!) for a while. I only found this one a few days ago (Great timing by the way...I just joined this forum today)
Anyways, there's one
here. It's called StudyCard Studio Lite.
It's freeware, the usage at first was sorta confusing, but if you read through the directions it's easy enough.
(Have you done the thing in System Preferences so you can write in Japanese? Because you need that...)
When you open the program it will show you how to use it with this lengthy sort of introduction (ugh, how I hate instructions) but the thing is useful.