Yggdrasil

Yggdrasil is the dragon of creation with which Mononobe Yuu has a contract. Yggdrasil's only desire is the destruction of all other dragons which runs along with Yuu's wish to protect all those around him. The use of Yggdrasil's power does not come free though, as Mononobe Yuu must pay with his memories to attain more power as it becomes necessary to defeat stronger dragons.