Ragnarok, Volume 5

The golden city of Prontera is under attack from Himmelmez, a Valkyrie and necromancer who commands the armies of Nilfheim. Her master, Freya, seeks the pieces of Ymir's heart, Midgard's lifeforce, in order to ensure that her reign will last another 1,000 years. Chaos and his companions enter Himmelmez's flying fortress to stop the Valkyrie, but they'll need the assistance of Loki if they hope to come out alive.