Blitz Ace

[TheSpoonyBard]

In addition to the choices made in the plot, actions in battle also affects which girl will be selected. If Tidus heals, cures, uses Guard/Sentinel, etc. on her often, the affection level will rise. You can cause the affection level to fall if you fail to cure statuses, leave the girl KO'd, use a Petrify Grenade and shatter the girl, and so on.

However, if a girl is incapacitated in some way (KO'd, petrified) then the girl with the next highest affection level will throw the ball. If all are incapacitated or absent for story reasons, the ball will come out of nowhere. Similarly, if you use Blitz Ace underwater, Rikku will throw the ball. If Rikku doesn't have the highest affection level, the ball will come out of nowhere.

Also, the ball will always be thrown by a female character.