At the Cutscene after defeating Shuyin at the end of X-2, If you hold X ( or triangle i cant remember) when Yuna is stood in the Flower bed at the Farplane, a secret Cutscene appears showing Tidus appear and holds Yuna telling her everythings alright and then disappears into thin air, meaning Tidus still exists in Spira(or the farplane, its complicated)