Set in the land of Yuguto, the people thought that the land they live is the size of the world, but it's actually divided into several areas, each with a respective king. Even though there were small wars among areas, the kings had roundtable meetings to maintain peace and balance. It was until a dark group of dark monsters appeared... (Source: MAL News)

Kyou kara Maou! revolves around Yuri Shibuya, your average Japanese teenager. One day, Yuri sees a classmate being harassed by bullies. Thanks to this intervention, his friend is able to escape, but unfortunately Yuri becomes the new target of the bullies in the process and gets his head shoved into a toilet. But instead of water, the toilet contains a swirling portal that sucks him into another world, largely resembling medieval Europe. There, he is told that he will become the next Demon King due to his black hair and black eyes, traits only possessed by the demon's royal lineage. Yuri's arrival is met with some skepticism by some of the 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 be a true Demon King, as he tries to keep the peace between demons and humans in this strange new realm.

While on an errand in the forest, retired E-rank adventurer Belgrieve stumbles upon a basket that holds an abandoned baby girl. Taking pity on her, Belgrieve decides to adopt the infant and names her Angeline. Growing up, Angeline idolized her father, especially admiring his swordsmanship and wishing to become an adventurer just like Belgrieve once was. To fulfill this ambition, Angeline sets out to the royal capital. Over the years, she rises to S-rank, gaining the title of the Black-Haired Valkyrie. Despite surpassing her father, Angeline boasts about him and embellishes his exploits, generously calling him the Red Ogre. At last, the time for Angeline to go back home has come, but she quickly realizes that various evil forces persist in preventing her from returning to her beloved father's side.

Three months have passed since the Demon King was defeated by a hero. Mankind rejoices over their victory, but dwellers of the demon world do not share the same sentiment. With the loss of their king, they must now hold a tournament to decide who will become his successor. Monitoring the competition is the hot-headed yet powerful Vamirio—one of the Four Heavenly Kings. Among all the participants, she is extremely distrustful of one: Helck, a human hero who claims to hate humanity. As much as she wants to get rid of him, it is impossible due to Helck's incredible strength and popularity. Amidst the competition, Vamirio discovers that humans have vanished from various towns. As a result of this puzzling turn of events, Vamirio grows desperate to reveal Helck's true intentions by carefully crafting a plan to make Helck lose. If she proves to be successful, she might uncover where his loyalty truly lies before the demon world is endangered.