I (Scot) just got back from seeing the movie "The Chronicles of Narnia: Prince Caspian." I may write a fuller article about this later on, but for now let me give some quick impressions. First, is it any good? Yes, very. I wouldn't rank it with the "Lord of the Rings" movies, but it's definitely on par with the best of the Harry Potter movies. It's worth your time and money.
Also, though the book is a little bit lighter on the Christian themes than the first book, the movie actually has more. Part of this is because the writers re-structured the events of the book in order to add more dramatic tension, and yet, suprisingly, most of the really potent moments come from scenes written only for the movie. (mild spoiler alert) As a result, Aslan doesn't appear to the group. Instead, Lucy has to go off on her own to find him, whereupon the two have an amazing conversation about how Lucy had to take a step of faith and come to him, even though none of her friends and family were willing to do it. That conversation alone is worth taking your Japanese friends for. Also, when the white witch shows up in the movie (you've all seen it in the trailers), we are treated to another amazing moment.
Oh, and the movie has Reepicheep. If that doesn't mean anything to you, it will after you see the movie.
So, after my first viewing, I highly recommend it. Strictly as a movie, it's good. As an adaptation of a book, it shines. As a dialogue starter with Japanese friends, you don't want to miss this opportunity.