So the ally that the summoner chooses for Summoner Support is usually the one they count on the most, right?
You could put it that way. The summoner might lean toward an ally who sees a lot of action—their strongest ally or a Legendary Hero, for example.
But what about us? We're the ones who called Kiran to this world in the first place, aren't we? Why weren't WE chosen for Summoner Support?
Ack! W-well...maybe it's because we're already doing such a great job that we don't really need special support?
Do you really think so? In that case, we'll have to keep up the good work so that we can keep setting a good example!
(Phew. That was a close one...)
Strengthen Allies with Summoner Support
You can set up Summoner Support from the Interact with Allies menu to support one of your allies, creating a special bond between you and a Hero. You can choose only one ally to support at a time, or up to three allies if you're subscribed to Feh Pass. By having that ally defeat enemies of level 35 or higher, you can increase your Support Rank, which will in turn increase the stat boosts the Hero receives. You can change the ally you're supporting at any time, though doing so will reset your Support Rank.
Stat Effects per Support Rank
Rank C: HP+3, Res+2,
Rank B: HP+4, Def/Res+2
Rank A: HP+4, Spd/Def/Res+2
Rank S: HP+5, Atk/Spd/Def/Res+2
Choosing an Ally to Support
Typically, you'll want to choose to support your strongest allies who you often send into battle or colorless allies for their versatility. Legendary Heroes are some of the top candidates for Summoner Support, as you're likely to use them very frequently in Blessed Gardens maps or the Arena. Of course, there's nothing wrong with simply picking your favorite!