Have you heard of Namco NamjaTown?
They have famous gyoza stores from all over japan on its first level and desserts/icecream on the 2nd level.
I wrote a blog entry about this place over a year ago HERE
[If you dont know much abt this place, you should read my old blog entry first]
Anyway Namjatown has many events and last year in December, they had the One Piece Event
One piece is a manga currently running in Shonen Jump and has also been made into an anime
It is also the number 1 selling manga in Japan [according to Oricon Charts]