[LacusClyne]

^you can check the postage cost from your post office.
it's best to write in japanese, i honestly don't think ayu can read english that well.
and most companies will open up the letters, and some will even throw away the envelope, so please write your return addresss(which you want ayu to send back to) in your letter.

and do not send ayu any gifts, i can assure you that the staff will take it when opening the letter. your gift will never reach ayu.