Dazai was sent to Hogwarts for a mission from the port. Mori told him it was for a special reason. When Dazai arrived to hogwarts, he was supposed to learn magic. But since his ability, No Longer Human, nullifies other abilities, it works on magic too, meaning that he cannot work with magic either. Being one of the only people there that cannot perform magic, teachers, and even the principal, have tried several times, but he couldn't learn no matter what. But of course, this is only a mission.