Looking at the movie story (what I remember of at least^^;; ;) and "Yubiwa" lyrics, I think that the song is a message from Hitomi to Van :
***warning ! there may be spoilers...***
- "Wasurenaide, hitori ja nai"
(don't forget, you're not alone)
...was Hitomi's message to Van.
Van was a really lonely person before knowing Hitomi ; he thought that he would always be alone to face life and that he would never be able to escape fighting. But then Hitomi made him realize that she too was alone, and that together they could get through...
Hitomi really wanted Van not to feel alone anymore ; she wanted to relieve all his pain and sorrow... and be able to "see the blue sky with him once more" (it's what she said in a certain passage of the movie)...
- "Itsuka kitto aeru futari naraba"
(Someday the two of us will surely meet again)
...were Hitomi's last words to Van (not exactly said in the same way), at the end of the movie...
(many other things to talk about, but I'll stop here^^;; ;)
So, *Hitomi's point of view* wins ! \(^o^)/
... if you're interested, here
is a a great site about the "Escaflowne, a Girl in Gaea" symbolism... o____o