Kyou kara Maou! centers on Yuri Shibuya, an ordinary Japanese teenager. One day, Yuri witnesses a classmate being harassed by bullies. Because of his intervention, his friend manages to escape, but unfortunately Yuri becomes the new target of the bullies and has his head shoved into a toilet. Instead of water, however, the toilet contains a swirling portal that sucks him into another world, which largely resembles medieval Europe. There, he is told that he will become the next Demon King due to his black hair and black eyes, traits possessed only by the demon royal lineage. Yuri's arrival is met with some skepticism by certain demons, who view him as unworthy to be their king. However, after Yuri wins a duel by utilizing his magical powers, the demons slowly begin to acknowledge him as their monarch. Yuri must now learn what it takes to be a true Demon King, as he tries to keep the peace between demons and humans in this strange new realm.