A friend's 24 y/o son and his girlfriend have just booked flights and hotel in Japan (in October). They still suffer from the optimism of youth, and I'm not sure how much they've researched. A quick Google suggests that no visa or innoculations are required, but does anyone have a tips or advice that will be useful?

She's a graphic artist, they're both interested in Manga, and that's the main focus of their trip.