I got a -Spd Owain now (lucky), and all I plan to do with him is fodder him off. Looks like Ares is my best candidate. Second mention is Anna with her Noatun, and if I go with this one, I might have to kill my only Ylgr for Sorcery Blade (I'll explain jn another post).
Depends on your build for Ares. If you're doing DC/Vantage, Bonfire is a much better choice. His role is to get hit once and counter nuke every enemy on the team. Can't really get allies close when Ares is going to be at the other end of the map. Not to mention but the enemies need to target Ares, not his ally.
Why Ares? He's a horse unit and has nothing (in his base kit) that would make you feel compelled to keep him beside an Ally.
Sharena with her Bond Refine and Anna with he powers of teleportation are both Excellent candidates. L!Lyn would also be a great candidate too, but few would feel the desire to invest in her so eh.
Blue flame? That will sometimes be only an extra 10 dmg. Even when he is adjacent, it's only an extra 25 damage. Bonfire gives Ares an extra 15-17 flat damage with no adjacency condition. If he is in Brazen range, then it's an extra 18-20, even more if he Def is buffed. Draconic Aura gives him an extra ~17 Atk. This will scale with the weapon triangle and other skills so damage output varies.
I don't think Blue Flame is the best choice for him. He has adequate Def to just run Bonfire. Blue Flame is for units with poor bulk of any kind that still want flat damage to go against the weapon triangle.
Anna is a better choice, but I advise against foddering rare and powerful skills to units that will remain at +0.
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