Outside of Battle
There’s a few different things than can boost your support relationships at your castle, which you have access to after Chapter 6. After a battle, different characters will have exclamation points over their heads. Although it’s mostly random, talking to these characters can result in various things. Sometimes they’ll give you an item, sometimes they’ll ask for an accessory and sometimes it will just result in a relationship boost. This boost can happen between said character and the avatar, or between two characters who are talking.
When characters ask for an accessory and you give them one, this will also result in a relationship boost. The character will wear the item with boosts in castle invasions or online matches, but removing an accessory from a character doesn’t lower the relationship level in any way.
The avatar also has a function called “Invite Ally” when they visit their private quarters. This allows you to select one ally to come over and chat with. When selecting which ally some will have hearts next to their names, this means that a relationship boost will happen with this ally if they are invited over. You’re only able to invite allies when the time of day is afternoon or evening.