Final Fantasy X-2 is the first Final Fantasy game to continue a storyline from a previous Final Fantasy game, 'Final Fantasy X (2001) (VG)'. For this reason, despite being the twelfth game released in sequence and being labeled "X-2", the game is not considered Final Fantasy XII.
Squaresoft originally planned to make two spin off titles to 'Final Fantasy X (2001) (VG)'. One was to be focused on Yuna, and the other on Rikku. However, that idea was scrapped, and both characters play a central role in this game.
There are four possible endings to the game, depending on the player's actions during the game and their defeat of the final boss. The best or "perfect" ending can only be obtained by getting a 100% completion rate.
Rick Gomez and George Newbern would later be chosen as the official voice actors for Zack Fair and Sephiroth respectively in the Compilation of Final Fantasy VII. In both Final Fantasy titles they appear in, they voice military men. George Newbern's character goes mad and betrays his comrades in both as well.
The two guards in the opening AMV that Rikku and Paine decapacitate are Biggs and Wedge, two guards in the first game that stand outside of the Luca stadium lockers. Biggs and Wedge could be recruited for blitzball.
According to developers, the reason Lulu wasn't included in the main party is because - as a surrogate older sister to Yuna, the latter would have relied on her too much and she wouldn't have been able to find herself throughout the story. This is acknowledged in the game with Lulu's line "I'm not there any more. So now you can spread your wings."
This game expands on several of the minor characters' stories from the first game. Kimahri Ronso becomes the elder of the Ronso tribe; Wakka and Lulu are having a baby; Brother (the pilot of Cid's airship in 'Final Fantasy X (2001) (VG)') plays a much larger role, being the pilot of the Gullwings' airship; and the other summoners, Dona and Isaaru, who were on their pilgrimages two years ago are finding their own new paths in life.
Cree Summer voices two characters in this game, having voiced two in the previous one. In both games she voices a summoner and a young child - Belgemine and the young Tidus in the first game, Lenne and Calli in the second. Calli had been voiced by a different actress in the first game.
A prequel game was considered as well - focusing on the pilgrimage of Braska, Jecht and Auron. It was decided that would be too repetitive and developers incorporated their ideas for that into this game instead.
Paine's costume when she wears the Songstress dressphere is drastically different to the other two. This is because developers couldn't decide if she should be "rock and roll or Top 40" - and went with a combination of both.
The trivia item below may give away important plot points.
Some fans believe that Tidus originated from the Fayth's Dreaming of Shuyin, which is why the two bear so many similarities. Perhaps their differences could be attributed to the Dream taking on some of its own sentience, decomposing memories, or the desire for change.