This was a song, from the album
Fire of Unknown Origin (it has "Burnin' For You"), written by Eric Bloom (lead singer of BoC) and Michael Moorcock, a known science fiction/fantasy author. It was not written for the soundtrack of the animated film
Heavy Metal, unlike several other songs on the album, but ended up being the one the director picked to use.
If you see the name Michael Moorcock and it rings a bell in your head, that's because he was the author of The Elric Saga, a high fantasy book series that was part of the personal reading diet of one Hironobu Sakaguchi around 1986 or so. In other words, it is the series of books which were Sakaguchi's favorite fantasy novels, at the time that Final Fantasy 1 was made.
It is extremely weird to me, that the lyrics in this song sound exactly like what Cloud goes through in FF7, but it absolutely is probably a coincidence. One of those 'six degrees of separation" things.