[TokuChris]

The history of Helheim is pretty much this:

- The forest grows in to other dimensions
- The ruler of the current dimension eventually must give the Golden Fruit of Knowledge to a new ruler of the dimension that the forest has "invaded"
- That ruler then has the choice to make - save himself and let his world be destroyed, or sacrifice himself to let the world be saved. Apparently no Overlord has ever chosen their world over themselves, though Roshuo seems to have some regret at his "queen" dying as he took over Helheim

It's like a cycle of destruction. The forest expands and each time it expands a world is lost in the process because the chosen one of the forest always chooses themselves over the worlds they live in.

Kouta is choosing the world over himself. This will, in essence, end the cycle of destruction and eliminate like ... everything.