In the original version, its license costs 90 LP. In the Zodiac versions, its license costs 100 LP and it can be used by the Knight and the Red Battlemage, although the latter must unlock Zodiark to reach it on the License Board.
Ragnarok is a weapon.
Ragnarok has a sprite.
Ragnarök is an event in Norse mythology that is similar to the Apocalypse. It is an event that is set off by the death of the god Balder, which was orchestrated by Loki. The Ragnarok was a final clash of all the major entities of Norse mythology. This caused all of the human spirits up in Valhalla to come down for the final battle.
This bloody encounter ebbs with the destruction of the universe and Balder along with a little handful of entities that are put in the bodies of children and only contain memories of the world before Ragnarok. Those entities would become mortal, and would live again in a new world of plenty and just existence.