Returns are handled by the store that took the order. Start there, with the order number, and the process will be faster than anything we can do from Tokyo. The store can issue a refund or a replacement; we cannot.
A blind box that contains a design you did not want is not a fault. That is the mechanism working as described, printed on the pack and explained on every product page here. Collectors trade duplicates with each other and that is the intended route.
A genuine fault looks different: a missing part, a cracked moulding, a paint pass that has skipped a face, a cup-rim hook that will not hold on any glass. If you have one of those, photograph it before anything else — the store will ask, and so will we if the question reaches us.
Where a fault turns out to be a production problem rather than a transit one, we want to know. Write to [email protected] with the series name and the photograph. It will not get your money back any faster, but it is how a mould gets fixed before the next run.