Which Final Fantasy game is set in the world of Ivalice and follows Vaan?

Final Fantasy XII is the game set in Ivalice that follows Vaan.

Released in 2006, Final Fantasy XII takes place in the kingdom of Dalmasca and neighboring regions of Ivalice. Vaan is a young orphan from Rabanastre who dreams of becoming a sky pirate. His life changes when he becomes entangled with Princess Ashe, the resistance against the Archadian Empire, and a struggle over Dalmasca's future.

Vaan is the viewpoint character and an important member of the party, but the political story also gives major weight to Ashe, Basch, Balthier, and Fran. This ensemble structure can make the answer less obvious than in games centered more directly on a single hero.

Ivalice is not exclusive to Final Fantasy XII. It originated as the setting of Final Fantasy Tactics and later appeared in other games, including Final Fantasy XII: Revenant Wings and Final Fantasy Tactics A2. The other options are different mainline entries: Final Fantasy XV follows Noctis, Final Fantasy XIII follows Lightning, and Final Fantasy IX follows Zidane.