Kira is kind of a better version of Maxwell, except the bonus damage is light/dark as opposed to all for Maxwell (but the crit damage is all).
Leader skill: 150% crit damage and 125% element damage dark/light (Kira); 125% crit damage and 100% element damage all (Maxwell)
BB: 60% crit and ignore defense (Kira); nothing for Maxwell
SBB: 60% crit, ignore defense, and attack down (Kira); 30% crit (Maxwell)
Plus you get the added bonus of 7* versus 6* so much higher stats, and about double the imp cap. Damage is 280%/500% on BB/SBB for Kira, and 250%/660% on BB/SBB for Maxwell. 1200% on UBB for Kira.
Kanon is kind of like a beefed up Narza, but the mitigation is UBB. I actually haven't used Kanon, but people swear that it's an amazing unit.
With Kira, I'd build a team like this: Kira (lead - crit buff), Elza (spark), Maxwell, Feeva (attack/BC), Cardes. Without Feeva, you could probably sub in Atro (attack/def), Magress (def), Zergel (attack), Kuda (attack), or Ardin.