Chayula's Grasp Rare Finisher Effect not working

I bought a "Chayula's Grasp Rare Finisher Effect"
and set it to my character slot in the store,
but it's not working.
I've also restarted the game and adjusted the game display settings.
I'm a CoC Blood Mage with a Sphere.
I'm wondering if I set it up incorrectly,
or if spells can't use the Finisher effect.

I'd appreciate any help.

It is found that the probability of seeing this effect is very low