General

I just use Freezing Breath because it completely removes my hitbox, plus it gives the rest of the party a window to heal and attack.

well in my case(pally) i dont die from the full screen attack if im 100% hp, but i always try to get hit by the small lazor(dark genesis), bcuz u can tell wich is the big one and the small one if u pay attention to the ground, the big one does a bigger animation on the ground(like a volcano), so try to avoid the big one bcuz its a 1hko, but the small one is less, so try to get hit by the small one and use power elixir right after that and you'll be fine.

Alright thanks for the info guys, I'm sure tomorrow will be the day I finally kill empress

Also the full map gen is only cast after right after one of her knights is killed, or after V2. Yellow tests that says "Something something empress rage." So you actually can know for certain when she is going to cast it. Just end after killing one of her knights with full HP, and keep it full.

Sometimes there isn't a safe spot due to the placement, but if you look at the corners the safe spot is gonna be there if there is one. Just remember that after every summon first thing she does is almost always a full map Dark Genesis followed very shortly by DR because summoning a v1 or the v2 instructors resets her DR timer/CD and you'll be fine.

It's 90%, therefore you can survive it simply by being at full HP.

Empress casts the full map dark genesis six times in total.

Once after you defeat each of the V1s, not quite in this order, but you get the idea.

1. Mihile
2. Irena
3. Oz
4. Hawkeye
5. Eckhart

And once more after the V2s.

6. Mihile/Irena/Oz/Hawkeye/Eckhart

As the others pointed out, it's also not quite "full map", it just has a very large range. If you lure Empress to one of the corners, you can dodge it by running to the other corner. Though, fair warning, if you get caught between two beams while running you'll get hit by both, making it a 1hko.