Balmung was a magical two-handed sword wielded by Emperor Alric of the Cath Bruig Empire. The sword is arguably one of the most powerful artifacts in the Myth world. The sword allowed it's wielder to be immune to its own lightning, and the lightning from the sword would spring out and strike enemies down via a chain lightning technique. The sword also allowed the wielder to strike faster and with more power.
It is unknown which Emperor this blade actually belonged to, but given that it was found in the catacombs of the Cath Bruig, it was probably Emperor Clovis' sword and was buried with him along with the Ibis Crown. It is unknown if this sword was ever repaired, but Soulblighter broke the blade when Alric and him fought at the foot of Tharsis.
GURPS has stated that Balmung is rumored to be highly intelligent and has a mind of its own. GURPS stateds that Balmung will sometimes try to possess the wielder, however, Alric proved immune to this affect if this is true as Alric did what he wanted with the blade.