During Battle
This is the easiest and most common way you’ll build support relationships in Fire Emblem Fates. Positioning of your units on the field is everything, and you want to make sure to have characters that can build support next to each other.
By checking the list of relationships in the menu before a chapter you can see who will work best with who. When characters stand next to each other in battle, they’ll join in when attacking or defending against an enemy. For every “action” taken like attacking or healing, as long as two characters that can build support are next to each other, a heart will appear over their heads after the action. This signifies an increase in their bond. By positioning characters together, the main one attacking or defending will receive a boost in stats like hit and evasion.
Additionally, you can pair two characters into one unit. You’re able to switch which one you’ll want attacking and supporting, but this is a good way to build a support between a character with high defense and one with low defense. The more you use units together in battle, the more support conversations you’ll be able to prompt, causing two characters support level to go even higher.