The first form of the Soul Slayer War Arts— Vortex of Lost Souls—and the second form— Vortex of Astral Souls—that Evan had used against Velgoth in the Azragoth World are intrinsically connected.
The second form is entirely dependents on the first; without it, the second form can't be activated.
However, the third form of the Soul Slayer War Arts is completely different from the previous two.
Unlike the first form, where one literally pulls out the soul of the target and traps it within the Halberd of Destruction—later using the captured soul through the second form—the third form operates on a completely different level.
As its name—Annihilation—suggests, the third form is the embodiment of pure destruction.
Because the current Halberd of Destruction that Evan possessed was only a replica, he only had access to the knowledge of the first three forms of the Soul Slayer War Arts.
