Sora is a character in Escaflowne: A Girl in Gaea. Her name means "sky" in Japanese. She did not appear in the TV series.
She serves Lord Folken, and has clairvoyant powers: she can sense where Hitomi is, and in fact summoned her to Gaea in the first place, by singing her mysterious song.
Some fans of the movie say that she is the Goddess of Wings, and Hitomi is merely a catalyst or tool that she used (or tried to use) to fulfil the prophecies. This idea makes sense if you watch the movie through with this in mind.
Sora's song is not Japanese; it is apparently an old Fanelian folk song.
Win dain a lotica
En val tu ri
Si lo ta
Fin dein a loluca
En dragu a sei lain
Vi fa-ru les shutai am
En riga-lint
Win chent a lotica
En val turi
Silota
Fin dein a loluca
Si katigura neuver
Floreria for chesti
Si entina
(instrumental)
Fontina Blu Cent
De cravi esca letisimo
Lalala…
De quantian
La finde reve
Win dain a lotica
En vai tu ri
Si lo ta
Fin dein a loluca
En dragu a sei lain
Vi fa-ru les shutai am
En riga-lint