I don't know how to perform an assist in co-op battles.
In co-op battles, when your Buddy is under attack, you can tap their icon to perform an assist.
Upon activation, you'll push your Buddy out of the way and become the target for the Boss' attacks for a short while.
Performing assists will also increase your Link.
By building up your Link, each player will gain the following bonuses once the Boss's Shield is destroyed.
----------------
・Ki Recovery UP
・Arts Card Draw Speed UP
----------------
If you can not find possible solutions from FAQ, please send your inquiry from below.
Please send your messages regarding our network contents via the following form. We will forward them to the relevant department.
We do not provide individual replies, but your messages will be passed on to the appropriate department.