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Chapter 4: Connect with Friends!
You can find new friends by choosing other player at the Support selection screen when starting a quest. You can send a friend request after the battle has ended. Also, a more practical way of adding friends is by sharing user IDs with them directly.
Looks like there are some Servants that can only be summoned through Friend Points.
Oh, is that so..?
Chapter 4: Connect with Friends!
by Riyo