Package held by customs / fanclub packet

Hello! I have sent a package to a fanclub of a group I like. The tracking says that the package is being held by customs.
The address of the group is a post office box in Tokyo.
I wonder why they are holding it because I just sent some papers and a couple of CDs which I declared to be 12€, which is what they costed to me.
I would like to know if the recipient will have to fill a declaration form or the package will be delivered safely at no extra costs. Because in case the recipient has to fill any custom forms or pay a tax for the customs, they will reject my package...

08/10/2016 19:30 Posting/Collection
08/13/2016 00:55 Dispatch from outward office of exchange
08/16/2016 15:28 Arrival at inward office of exchange KAWASAKIHIGASHI KANAGAWA
219-8799
08/17/2016 09:00 Held by import Customs KAWASAKIHIGASHI KANAGAWA
219-8799

Any ideas on the situation?
Thank you!

The recipient should be able to ask themselves at their local post office. And the recipient should have been aware of incoming customs and duties payable for items entering the country.

It got out of customs today (27 hours in customs in total). How can I know if they are going to charge anything? Does it say it in the tracking records in case they charge something? They appear like so:

08/10/2016 19:30 Posting/Collection
08/13/2016 00:55 Dispatch from outward office of exchange
08/16/2016 15:28 Arrival at inward office of exchange KAWASAKIHIGASHI KANAGAWA
219-8799
08/17/2016 09:00 Held by import Customs KAWASAKIHIGASHI KANAGAWA
219-8799
08/18/2016 12:30 Departure from inward office of exchange KAWASAKIHIGASHI KANAGAWA
219-8799

If you marked the contents as "gift," and since the value is small, I don't think they will charge/impose any taxes, either import duties or consumption taxes.

I don't think the tracking will show if there was any charge, but in case the recipient rejects it, it will appear as so. So unless that line appears, I would not worry; I would safely assume that they received it alright when the "delivery completed" line appears.

Thank you, you are right. It went through and today it has arrived at its destination.