Visit Kintaijin just outside the Stakato Nest (hunting areas from Rune). He will offer two quests. You need to complete I'm the Only One You Can Trust first. It is an easy quest to complete. Head inside the nest and hunt monsters until you have 25 claws. Then return to Kintaijin and you can start the second quest he offers: Only What Remains.
You will go back inside the nest and kill more Stakato until you gather 500 dirty bead. Take the dirty beads back to Kintaijin. He will give you a syringe. He will also give you some treasure chests with adena, festval adena, element stones, and maybe enchant scrolls. Take the syringe back inside to a cocoon and use it to spawn a boss mob which will give you a cocoon that may contain forgotten spellbooks.
This quest is repeatable.