Phantom speed seal + wing sword?

Yes. Phantom spd works with any skill requirements that involves spd.

I'm pretty sure it works, but Caeda's spd is already high enough that with the proper A skill and party support she should have more spd than nearly any defending unit... And if she doesn't, an spd seal should be enough to solve it while helping secure more doubles. Although fixing her meager atk is probably more important than further increasing her already high speed, especially when up against armored foes.

However, I think that giving her a ploy seal is probably the best option, given how high her RES is.

A +spd , caeda with fury is 43 spd. With 3 allies with goad flyers she is at 55 spd. Thats how i run her and she always triggers the wing sword cooldown effect.

I run ploy skill seals as shes at neutral 37 res with fury.