The Thunder Rune is the higher level of the Lightning Rune. With its aid some of natures most powerful electrical discharges can be called down upon a single enemy or in some cases also on several enemies. The highest level magic of this rune, usually Thunder Storm, also varied in its effects from game to game, sometimes targeting a single enemy and other times several.
During the Gate Rune Wars Grenseal comes equipped with a Thunder Rune, permanently attached to his hand. Further optional of these crystals can only be found very late in the game, hidden a chest in Shasarazade or as loot from Simurghs near Gregminster. The wizard Mazus has one of these as well. In the enemy army the Commander of Highland, Culgan, bears a Thunder Rune, which can also be looted from him. And even in times of the Sun Rune Wars several rune pieces are scattered throughout the land, from which a Thunder Rune may be forged. - Celes