by a fan named "tadanopianohiki" who posted on youtube his/her own piano version. It was pretty much the best version of OWA I'd heard, but now it seems to have disappeared.

I found this post, but the megaupload links are now seized by the gov't.
Thread 79819

If anyone could find this, you'd be doing me and everyone else who loves this song a huge favor. I can't believe such a beautiful version of the song has been lost on the internet.