Black Lilith - Ikusa Otome Suvia

The protagonist Loki, a divine being, joins forces with the jotnar and denizens of Hel and invades Asgard, the world where the gods dwell. Just when it seems he has the whole world in his hands, Odin, the chief of the divine, takes a life-threatening measure. He seals the mouth of the river that feeds Yggdrasil, the tree which supports the world, and compels his captors, "Release me if thou wishest not perish with me."
The withering of Yggdrasil means the end of the world.
Our protagonist has fallen into a dilemma, but there are keys with which to break the seal on the gate. He discovers that those keys are sealed within the virgin wombs of the battle maidens who continue to oppose him stubbornly: Svia and Sigurd.