The Devil Is a Part-Timer! High School! Vol. 3 (manga)

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 both 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! Is there more between these two than they're willing to admit even to themselves?