The site is all in Japanese and they charge 2,100 yen for a box of 10 Kit Kats. If those are the larger boxes with two packs inside then that's a pretty fair price. If it's a box of 10 minis then I might balk. It's a super cute idea for party favors I think and I'm soooo tempted but I don't have any special occasions to warrant buying them. Maybe when I leave Japan I could give them as goodbye presents. Until then you'll find me perusing the pictures of Kit Kat boxes featuring newlyweds, babies, and small dogs.
Check it out - Chocollabo Kit Kat.