Onmyway-
I appologize for not responding to your PM from a while back. We were so wrapped up with our own Japan adoption. But, it sounds like you are on your way to Japan so, congrats!! We just returned and are still jetlagged (as I write this at 2:50am California time
) as well as adapting to life as a family of four!
Tokyo should have a copy of your I-171H. You'll still file the I-600 at the embassy there. You'll go back the following week for the exit interview and then most likely get your baby's visa the next day. Somewhat time consuming, but totally painless.
We loved Japan and can't wait to go back with both of our girls.
Best of luck to you!!! How old is your child? Boy or girl? How exciting!