Cast gloom at max energy, keep silence on at all times when fighting the lich, shieldgate to stay alivie, be carefull with your energy economy. Armor strip your sister with your 1 (liches can't be armor stripped), then cast sonar x3 to one shot him (you can also cast it less times) shotguns are recommended, like the kuva hek or the cedo, to bypass the adaptive dmg reduction from the lich/sister. The more multishot a weapon has, the better
Can replace [Brief Respite] for [Growing Power] to help with gloom slow