Nube is a 25-year-old man with two jobs. First off, he's a powerful exorcist who deals with the affairs between humans and youkai in his adopted home in Doumori. Second, and just as importantly, he's the teacher of class 5-3 of Doumori Elementary, both guiding and protecting them from the spiritual encounters they face. Both jobs are equal and important to him in their own ways: he chooses to protect the innocent and punish the wicked, both human and youkai, focusing primarily on those still young and innocent enough to have the need of a guardian.
He is well versed in exorcism tools, but his main weapon is the "Oni no te," a real oni that was sealed in Nube's left arm (in the anime, his arm is possessed; in the manga it's completely merged).