I said in other threads that I donīt believed that the little monster inside Sin was Yu Yevon.
He is somewhere on the world disguised.
So where he is?
He was allways there on Macalania Forest.He plays songs and summon dreams including a bunch of colorful butterflyes.He desguise as a person from the bird race.He also summons treasure chests.He is a central figure there(can even be seen from afar).It is obvious he summons dreams.He is probably of the bard job.He even "sits" right below the weapon charging flower.And this place is way too mystical.
Itīs this place that appear on the last minigame before the final boss.
I will post other evidences as you post.