The Ancient Sword uses the Lightsaber skill. With the Lightsaber skill using Brawn (2), the Ancient Sword deals 4 damage. Now, if the Lightsaber skill is tied to Willpower (5) via Niman Technique, should the Ancient Sword still only deal 4 damage? Or should it go up to 7?

I think the Ancient Sword still deals the 4 Damage, Niman Technique refers to using Willpower instead of Brawn when making the Skill Check. The Ancient Sword has the +2 Damage which the corebook indicates that Brawn is added to total Damage dealt.

The damage dealt would be brawn+2+successes on the will+lightsaber skill roll. So if they roll 3 successes it is Brawn+2+3

Ok thank you both. I just thought it was weird that it would use the Lightsaber skill but still use Brawn for damage, irrespective of what the Lightsaber skill is using.

Cleared it up at least!

Yeah, the Ancient Sword is a Melee weapon, which means it follows all the normal rules for melee weapons, except that it uses your Lightsaber skill pool. So Brawn is added to the damage just like any other normal Melee weapon.

If it helps, you could consider the facts that Melee keys off the Brawn characteristic and that Melee weapons use Brawn to add to damage to be a happy coincidence, rather than contingent upon each other.