Hataraku Maou-sama! High School! Series by Satoshi Wagahara, Kurone Mishima

In this spin-off of the popular novel series, the devil king Satan and hero Emilia are reincarnated after their terrible battle--as high school students in modern-day Japan! Add in the innocent Chiho, a fellow student with a crush on the former lord of darkness, and you've got a romantic comedy of epic proportions!

Maou (aka the Devil King) and Emi (aka Emilia the Hero) have arrived from another world--and now they're in high school! Things are crazy enough already with classmate Chiho's ongoing crush on Maou, but are these kids going to be ready when a little girl shows up on Maou's doorstep and calls him Papa?

The Devil King and the Hero have found themselves flung from their world into ours--now they're just Maou and Emi, high school students in modern Japan. They've each got their sights set on becoming president of the student council, and sparks fly as their campaigns get rolling! But when the two get a little too up in each other's faces at the summer festival, their fellow student Chiho (with her crush on Maou) can remain silent no longer!

The Devil King and the Hero clash in an epic battle--in high school? Maou and Emi's latest feud centers on the race for student council president. The day of the election has arrived, but what will happen when the truth of Chiho's long-held crush on Maou comes to light? If only high school were as easy as a demonic reign of terror!

Having been banished to modern-day Japan to attend high school, the Devil King (Maou) and the Hero (Emi) have been fighting a high-stakes battle to control the student council! When Maou manages to win, the defeated Emi feels a terrible pang in her chest for...Maou?! Surely not! Did the high school foibles of these fated rivals just get a lot more complicated?