Quote Originally Posted by Unregistered View Post
dumb newbie question: Are eidolon effects passive effects?
Yes. The ones in your MAIN SLOT only, plus the one in your friend slot.

Eidolons also have a different, active effect that happens when you summon them. If you pick a person who is on your Friend List to your friend slot, then you get that Eidolon usable at the start of the fight.