Yggdrasil is the dragon Mononobe Yuu contracted with—basically the creation dragon itself. Its whole thing is wanting to destroy every other dragon out there, which actually lines up pretty well with Yuu's goal of protecting the people around him. The catch is brutal though: every time Yuu needs to tap into Yggdrasil's power to fight stronger dragons, he has to pay for it with his own memories. The stronger the power he needs, the more he loses.
Content compiled by AnimeList.moe from publicly available sources.
