I've already played a game like that, as mentioned in this thread, the game you mention is FFXII. Vaan is the player character, but he is literally just along for the ride. The story is all about Ashe, and the short bits where you don't have Ashe are either A) The start of the game showing how Vaan bumbled his way into things, or B) Vaan is being the sidekick of Balthier/Vossler to go save Ashe for a short bit. Barring these two events, Ashe is the start of the show front and center. And when she's not the star of the show, Balthier is. (Rightfully so, my GOD I love Balthier)
And everything aside, I adore FFXII for this fact, not to mention all the other reasons I have to like it, like a spiffy combat system and interesting politics based story instead of what became the standard for JRPGs outside SMT releases.