Delthea pity breaker

Delthea has more attack (like 1 point more), more speed, has a Hone Melee tome, and comes with Death Blow 3...

Micaiah has more defense and resistance, comes with Anti Armor/Cavalry tome, Distant Defense, Guard, and a Spur Attack...

I think it's safe to assume why Delthea has a better rating.

Congratulations on obtaining her best IVs!
She is a really useful blue mage.

Offensively speaking, Delthea will be overall more reliable as Micaiah relies on the bonus damage from Thani against amors and cavalry, whereas Delthea has simple raw power and speed from the get go. Micaiah is simply able to tank ranged damage better and suited to take out prevalent threats through her tomes bonus damage, so the meta is more tailored to Micaiah being effective rather than Delthea.

They fill different roles, Delthea will still be a fantastic blue mage who can offensively support allies and be a powerful glass cannon of her own.

I had the same thing happen to me back when I was trying to get Bikini Corrin for my Birthday. (Like pretty much all the other seasonal units.....I didn't get her...) But Delthea is a major powerhouse and you will not regret that you got her, because I know that I sure don't.

Delthea is definitely a fantastic blue mage. I find Micaiah great in arena due to her weapon being super effective against armoured units which are rampant in arena. It isn't much of loss that you didn't get Micaiah as you got one of the best blue mages in Delthea.

As a pitybreaker, that's not too bad, as they go.

*glares at my +4 Merric*

Because Delthea's res is actually pretty bad, LnD Desp ArdSac is actually viable on her, with a Blade tome. I usually run that over Fury, though it's pretty good as well.

However, if you want to use her as a buffer, than Fury will probably do you better(she'll survive more engagements, and may be able to tank a singular magic attack). Draconic Aura is pretty optimal on her for Arena. If you want to use her in PvE, then Dragon Fang might be considered a better idea(nets you a lot more ORKOs).

Repo is not the optimal support skill for glass cannon mages: usually, Draw Back is considered a better option, though I suppose it really depends on your team. Repo is for calvary/fliers/tank units, and isn't as suited for glass cannons because it may put you in the line of fire.

For a C slot, you can't really go wrong with Drive Attack, though I guess it really depends per team: you could go double BoL for utility, or something of that sort.

That's a pretty solid pitybreaker.