The story line for FFX-2? Ok I can tell you what is going on briefly. But there will be spoiler...
Basically after Yuna and her guardians has defeated Sin and Yu Yevon, Tidus disappears because he is actually part of a dream of the fayths (when Yu Yevon is gone, so are the fayths). This left Yuna heartbroken and was determined to find Tidus at all cost after she saw a sphere of tidus 2 years after Sin is gone.
Also since Yu Yevon is gone, the use of machina has been encouraged, and Spira has started to become 'modern'.
So now in FFX-2 Yuna joins Rikku to collect all types of spheres around Spira and also to find Tidus if possible. There is also a new character called Paine who joins in Yuna's party.
