The princess quest requires players to go through battles at Muspelheim map to seek for the new precious material called Succubus Emblem in order to help Delilah re-seize the throne from her relative - the Unrightful Ruler Sarah. The material is only dropped in the battle against Sarah. After completing the quest, players will be rewarded with the new heroine herself with powerful stats and skills.
Appirits noted that the quest will be available for all players to undertake and expire after the event's end date. It is recommended that players take the chance to obtain one of the most powerful unit in Einherjar - The Viking's Blood without using the Summon feature.
A review of Einherjar can be found here.