In the original, it sounded like (and still sounds like to me, even though I have listened to the attack many times to hear exactly what he is saying) Sin Harvest Angel. I have heard that so many times, listening for the "Descend Heartless", but 500 attempts later it still sounds like "Sin Harvest". Which sounds better anyway, so I don't much care.

But in KHII he definitely says "Descend Heartless Angel".

Anyway, Sephy isn't that hard in either game if you know his patterns and how to counter them.