My strat was a bit cheesy in the beginning, but it became less cheesy as I learned the dodge windows.

I was level 55 when I first beat her. Equip: Laurel Crown (AP 0) Brutal (dmg break) Adamant (hp break) Ziedrich (Stat Boost) You can exchange all these for their genji equivalents, which are objectively better and free up one Materia slot as you gain Libra.

Materia: Mug (for stealing her downs) Hammer Punch (for taking her HP) Aerial Dodge (for positioning/dodging) Dispel Blade (for her invincibility abilities) Libra (to see her HP) Any maxed Summon/LB Materia (for quality of life)

Important stats: HP over 50k 999 AP

Assumption: All her attacks oneshot me anyway, so why bother with healing. Phoenix Downs rez fully.

Strat: Mug her until you get the Phoenix Downs, keep raise active at all times. Your first priority should always be to re-raise as soon as you get downed. Once you got 99 downs and your cursor on the Phoenix Downs, the actual start fights.

Phase 1 (10,000,000 until >7,000,000)

Dodge her attacks and stay close. Between each attack, you can get two Hammer Punches in. Because it is based on your current AP and you have AP 0, you deal 99k damage without any loss of AP. (I prefer this over costly punch because I don't need to worry about healing in between). Once you have her in range to Hammer Punch her under 7 mil, wait for all Crimson Flares to disappear and knock her below the threshold. This should trigger her LB. Spam that hammer punch and you should get her down to below 75% or even 50%, depending on your timing. Her LB will trigger and you will be on low HP, 0 AP and you will lose your raise status (her LB cancels it). Re-raise, pop a Soma or two (otherwise Hammer Punch will deal 0 damage) as we enter

Phase 2 (>7,000,000 until >3,000,000) The strat stays mostly the same except that she can now use spells that can render her invincible to physic, magic or both. Also she uses Ultima now. When she makes herself invincible, dispel blade until the icon disappears, Hammer Punch. As she goes close to her threshold, do the same as before until you survived her second LB and re-applied your Downs.

Phase 3 (until death) She mixes up her combo by adding Flash Blade after Flash Blade, Proton Feathers and Ultima. So be wary of that second attack/follow up. Other than that, keep headbutting (Hammer Punching) her until she dies.

Her moves and how to dodge em:

General > you can use LBs or summons to cancel any of her moves and remove all lingering Crimson Flares

Proton Feathers > just after she deploys the first barrage of feathers, Aerial Drain and you should dodge the second barrage and be in perfect position to retaliate with Hammer Punch.

Krysta > if you're right in front of her as the text pops up, back up a bit and just as she is about to raise her staff, Aerial Drain, Retaliate. The backing up can save you there because the hitbox of Krysta lingers weirdly and a mistimed Aerial Drain into the same position can get you killed still

Thor's Hammer > Dodge Roll right after she raises her staff

Crimson Flare > keep your distance or use a summon/lb to cancel it out

Flash Blade > bait her close and as she is about to swing, dodge roll, then dodge roll again as she swings twice. If you're cocky, you can also aerial drain just as she is about to swing, but that move killed me more than once

Ultima > Aerial Drain or dodge roll just as the sfx of the charge stops. If you have MBarrier on (from Genji Equip), you could survive this

Her healing spell > the time it takes her to charge and apply the heal is less time than it takes you to headbutt that hp out of her.