Executioner's Blade!!!
It was a replication of Allura's famed attack but without the power of Velouria's blessing.
However, in order to achieve the same effect, Alice had to overlap several theories and attacks that she's accumulated thus far.
First, the use of her blood mirrors compacted into a single sheet to increase the speed of the slash. Replication of Allura's instant slash.
Second, achieving the power to penetrate defence via rotational power but rather than a spiralling motion, it's a vertical circle like a saw blade.
Third, weakening defences through absorption using the abilities gained from activating her First Resonance.
With all three conditions lined up, she was able to replicate the potency and properties of Allura's Executioner's Blade to a certain extent!