I beat it. Surprisingly, the tail is the hardest of the four or five final battles... I managed to die a couple of times today before beating it. Then I beat the legs, then the core, then finally Shuyin controlling the head... A cutscene followed, in which Yuna was just about to turn a weakened Shuyin with Lenne's words of love... But Shuyin realised Yuna was not Lenne, and attacked. Another easy battle for Yuna's special dressphere, and it was time for the ending. Lenne's ghost separated from Yuna and reunited with Shuyin, they could finally rest together...
Peace was restored to Spira, all was well. Nooj, Baralai and Gippal talked to the populace, giving Yuna's best, as she'd decided to leave. Then we got Yuna, Rikku and Paine on the airship, heading home. I was expecting my "good ending," but nothing more happened... I looked it up and apparently I'd needed to press "X" while we were on the flower field on our way back. Well, whatever. Redid the last battles again and pressed it. The little fayth (I suppose Shinra) appeared and asked me if I wanted Tidus back. I said "Yes!" and he said he'd do what he can. And then I got an extra scene after the ending - Tidus being "born" in the middle of the sea near Besaid, and heading to the shore, only to have the airship descend upon him and Yuna jump from it and into his arms... Cute. Then Wakka and everyone showed up and they were, of course, all happy. Tidus had come back. No doubt he and Yuna lived happily ever after. Yuna was really beautiful in this scene (it was FMV).
I then looked up the other endings on YouTube... For getting 100%, apparently you get an extra scene with Yuna and Tidus during a sunset. Nothing very important in addition to the "good" ending I got. Funnily, this scene's sea waves background noise plays every time when the "The End" screen is shown. So I suppose this is what the ending should be... Yeah, right, I'm supposed to get 100% normally? Not possible. Would've got the first ending I saw if I played normally, so not even reborn Tidus.
Well... That was relatively fun. Can't say this game impressed me very much, but the battle system was nice, at least.