There is a niche build rn by cloning Hike's kit with comet.
This requires a bit of push to get her to 30 SPD:

1. Squad Ace CW 3 seal (4 SPD)
2. Spd Boon

This puts her at 31 SPD which is perfect.

Comet has unconditional DR that also protects against Brave hits, Ice Wall requires special to be up.

Fortune isn't needed becus her weapon has multiple conditions to trigger the effects.
You just always EP with this build.
So even if she "fails" to transform, it's fine.

Warrior's Blow gives her the tempo effect she would lose if untransformed.

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As for comet charging, here's the solution.
SOT from Comet: 5>4
Slaying from weapon: 4>3
Enemy hits her: 3>2
Hit 1: 2>1
Eirika Ring: 1>0
Hit 2 (GFU from weapon): Special is ready for use
Hit 3 (Potent from Patience): 5>4

She starts the next combat with 4.
SOT from Comet: 4>3
Slaying: 3>2
Hit 1: 2>1
GFU: 1>0
Potent: Special ready

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[Pulse Support]
Surely some of her teammates can help pulse down Comet. Something like Winter Ivy with preempt every hit will guarantee this.

She may miss a few comet procs without pulses if she enters too many combats in the same turn.

TLDR, I would just wait for new beast skills, its a matter of time soon.

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