Thunder Magic is one of the three types of Anima magic. Thunder Magic has the lowest Hit% and highest Weight ratings, however, it has the highest critical ratings and Might of all the Anima Magic. The only exception to this is Fire Emblem: Radiant Dawn, in which it is weakest type of tome. It is composed of Thunder, Elthunder, Arcthunder, Bolting, Thoron, and Rexbolt, Rexbolt being the strongest, and Bolting having the longest range.
Being Anima Magic, Thunder Magic is strong against Light Magic and weak against Dark Magic. In the Anima magic circle, Thunder is strong against Fire and weak against Wind. Before being a magic archetype, Thunder was an anima spell in the GBA series, still holding the tradition of having a high critical ratio.
In Fire Emblem: Genealogy of the Holy War, it is average between fire and wind magic as the most useful, with having even might ratings with them, while having greater weight than wind, but less than fire, for tomes of the same level.
In Fire Emblem Awakening, Thunder magic is stronger than Fire or Wind Magic and still has that extra critical percentage, but it is also the least accurate of the three.