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if you're going player phase you don't really need QR seal anyways, go with atk/spd +3 or QP.

B slot works fine with swordbreaker, as chill speed is kind of expensive

C slot you can put panic ploy/atk smoke from the free kaze or even threaten res/threaten spd works fine if you're on a budget

in terms of specials, glimmer/moonbow are always reliable but bonfire works too.

you can slap on aether/galeforce for arena if you want, but you'll probably never get it off

Spd+3 Seal, Moonbow for Special, Panic Ploy or Threaten something.
Also, not strange at all.

I say that you should go with the Spd+3 seal to avoid as many doubles as possible. 40 Spd on initiation is pretty good for avoiding doubles, and if you can't kill the enemy, then the Dark Breath effect resolves and you debuff the unit for -7 Atk/Spd, which allows you to deal with them on Enemy Phase.

As for B-Slot, I think that Quick Riposte or Swordbreaker are solid options. Guard works if you really hate Bold Fighter Armor units or Slaying Edge + Wrath + Regnal Astra Ayra--mainly the Armors since I had a time where Zelgius was still able to hit through SB with his BF and proc Black Luna. Though, all of those skills are pretty expensive aside from SB.

C-Slot will depend on what your team needs, but a Drive skill, Smoke skill, or Panic Ploy are some good general ones. Threaten and Hone/Fortify skills are also great if you don't want to spend too much feathers / premium fodder.

Special can be Moonbow, Glimmer, or Bonfire for good damage. Aether also works, but you probably won't be seeing it proc too often.

If you want to try something weird, you can give your Nowi Knock Back as the B-Skill. (I have a very similar build on my +Spd F!Corrin.) The idea is that after attacking, you knock the enemy back a space--usually, it ends up within 2 space of its allies--and debuff everyone for -7 Atk/Spd. That way, you can guarantee that none of the enemy units with 47 or less Spd can double you (unless they have Brave weapons / Bold Fighter). You also cripple them so much that they can barely dent Nowi if they attack, considering that her mixed bulk is actually pretty decent. I think that this works extremely well with QR as the seal, but I have yet to test this out because my Corrin isn't in my main team, and QR is already reserved for my own Nowi. (Though, she is standard mixed tank with Steady Breath + QR build because I managed to pull one with the +Res / -HP.)