The address I used:
Hirokazu Yasuhara
c/o Nintendo Software Technology
5001 150th NE Avenue
Redmond, WA 98052
USA
He did misspell my name on the first one. The OCD in me kicks in and wants to correct it, but I don't want to mess with the original writing. Thoughts?
Tons of cash for postage later, (Japan is expensive) here they are:

He also drew Sonic on the back of the return envelope:
