Gaming Question about fire emblem awakening support ranks

[Chrisssj2]

Main characters can rank A,B,C ETc.

But avatar/dlc/spotpass characters can't get those ranks.

Though they are still able to trigger dual battles and help each other.

So what exactly is the use of support ranks? like what they do REALLY do?
I googled around and description is very vague to "bonuses" or "help" etc.. not rly explained.

 

[Arras]

They give the characters a stat boost when they're standing next to each other (mostly crit/hit/avoid afaik) and increases the bonus stats you gain from pairing them up by quite a bit. Like, if pairing up two characters would normally give you +4 strength (among other things), with a C rank it would be +5.

 

[Chrisssj2]

Thanks awesome! Really loving this game! Shame I missed Donnel and anna on paralogue 1 and 2.. cant get them anymore