Quote Originally Posted by Yazoo'squeen
I don't think Yuna and Lenne share the same spirit, to say. It's just the dress sphere that contains Lenne's spirit. Well, that's what I gathered from the game.
Yes, the Songstress dress sphere does contain Lenne's spirit, or something of her that she left behind. But remember, there are four people in the game that equip that dress sphere, and only one of them has the reactions that she has to it, many times at that. It would make no sense the these occurrences randomly only happen to Yuna. And one of the big themes of this game is the connections that so many things in the world of Spira share. Yuna and Lenne are somehow connected, and I just theorize they share the same spirit (or aura, or essence, or something). And I feel the same about Tidus and Shuyin.