The underworld gate has only opened twice in history. The first time it opened, the order of the Templar Knights found it. Hel quickly closed it before the Templars could sneak into her world.
50 years later, it opened again... Hel sent undead and demon troops to the human world to chaos and havoc in order to distract the gods from her real plan. But the 5 great kingdoms of the human world fought together. Hel took advantage of the distraction and sent her must cunning demon troops to the divine realm. She wanted to rule the divine realm and imprison all gods and giants.
But the God of Wisdom saw through her distraction. The God of Wisdom told the God of Light that Hel may want to take the Divine Realm and they decided to inform Odin. On their way to Gladsheim, many underworld soldiers stood in their way. Thanks to the help of the army of Divine Soldiers, they finally made it to the Bifrost. Unluckily, the Underworld Devil ambushed them there and injured the God of Wisdom terribly. But The God of Light killed the Underworld Devil, saving the God of Wisdom. Then he sealed the God of Wisdom’s power and sent him to the human world so the underworld creatures may never find him.