Phantasy Star II has a subtitle in Japan. In other versions of the game it was dropped. Roughly Translated it reads: "At The End Of Restoration". It has also been translated, as "At the End of the Time Which Can Never Be Returned".
The technique, Megid, is short for Megido. In The Bible, Megido, is a city that is associated with the end of the world, therefore, Megid is a technique of ultimate destruction.