Duel between Kas'im and Na'daz

During the years prior to Lord Kaan's rise to power, the Sith Empire was embroiled with infighting, Sith Lords constantly seeking to test their strength against the most powerful adversaries available; each other. It was into this climate that Kas'im was brought, taken from his enslaved parents as a baby and apprenticed to the Sith Lord Na'daz. Na'daz was a skilled duelist, specializing in lightsaber combat, and he trained his apprentice to be equally skilled. Over time, Kas'im began chafing under Na'daz's tutelage, and feeling he had learned all he could from his master, challenged him.

It is unknown where the duel took place or how long it lasted, but Kas'im was the ultimate victor. As Kas'im put it; As strong as he was in the Dark side, I was stronger. As skilled as he was with the lightsaber, I became better. Kas'im viewed the battle as a personal test of strength. He took Na'daz's lightsaber as a trophy.

Kas'im eventually joined the Brotherhood of Darkness established by Lord Kaan, becoming the lightsaber instructor at the Sith academy on Korriban. Ten years after the duel, he related the story to his prize pupil; Bane; and presented Na'daz's lightsaber to him as a gift. By that time, while Kas'im felt no guilt for killing his master, he considered doing so foolish, having accepted the Brotherhood's edicts regarding this; while he proved his own strength, he ultimately weakened the Sith as a whole, having deprived them of one of their greatest duelists.

Bane would later use the tale of this duel as one of the inspirations for his Rule of Two, a new Sith organization in which there would be only two Sith Lords at any one time; a master and an apprentice. In order to establish this new edict, Bane masterminded the fall of the Brotherhood of Darkness at the Seventh Battle of Ruusan. He killed Kas'im himself during their Duel on Lehon, as a personal test of strength.