And here we have it, we thought we'd get a new Colorless legendary

I think gray waves translation is not match with the japanese one.
The original also gives the highest buff to all of your stats.
ex: her atk tactics add +6 to a unit, if that unit danced, that unit will get +6 to all stats.

EDIT : It's actually her weapon.

they'd already said eir was going to be on the banner tho