|Wrath is a great skill, but the reduced cooldown does nothing for Owain; if the enemy attacks, Missiletainn automatically takes down 2 charges instead of 1, and Blue Flame only needs 2 CD to charge (Unless you're running something like Ignis, but why would you?). So, as long as you use him for enemy phase, all Wrath would add is the extra 10 damage. Now, that's always a huge benefit, but if we're not taking advantage of the extra cooldown, we could get the same results from just pumping up his Atk, and not relying on low HP lets him partner with healers or take on chain challenges with ease. So... let's redo Owain!
We'll be keeping Missiletainn and Blue Flame, of course. His A Passive, however, may change depending on what you want to do. Atk/Def Bond 3 ensure he gets that extra damage we talked about, while Spd/Def Bond 3 (Available from Ethlyn, a free Tempest Trials unit) will ensure he either always gets his second attack or can avoid some scarier doubles, like from speedsters such as Karla. It comes down to preference (And probably his IV; base 40 at +Spd will probably make Spd/Def Bond redundant). The goal, right now, is to get Owain to take a hit on enemy phase to instantly charge Blue Flame, then kill on his counter. Whether you need the second attack or the 5 extra damage is situational. I use Atk/Def Bond 3 myself, since my Owain is +Spd.
Owain's B Slot is variable. The most consistent option for this setup, though, is Swap in conjunction with Atk/Def Link 3. With that and either Bond discussed, Owain will have effective 42 Def. This can be boosted further with things like Drive Def 3, Close Guard 3, Summoner or Ally Supports, so on. If you were really crazy and got his Def above 50 like this, you'd actually outdamage Blue Flame with Bonfire, but that requires specific and unwieldy setups (And the animation isn't as cool! Come on, he's the hero!). The point is, Owain's taking hits like a champ, isn't reliant on Quick Riposte 3, and can have respectable Atk on top of Blue Flame. He has other options for this, like Chill Atk 3 if he wants to avoid damage and help the team, Atk/Spd Link 3 if he doesn't need the extra Def, Desperation 3 if you want to run mixed phase, or even his native Wrath, but Atk/Def Link is what I'd recommend myself. I would not recommend Vantage 3, however, as use of that skill interrupts the point of this set: instant Blue Flame.
Owain's C slot is pretty flexible and can usually go towards helping those other units he should always be adjacent to. Owain particularly appreciates having a Wave skill, as he can pass that onto his allies. Even Spd Wave 3 (Or Odd, up to you) works best with Atk/Def Link, but the decision is up to you in the end.
Owain's best option for a seal with this set is definitely Close Defense 3, as that in combination with his other buffs make him an extremely fast and durable threat. However, use of the seal always has heavy competition, so something like Spd/Def 2 is a great budget option.