Oni Gal-kun no Hara no Naka

Synopsis

Ritsu Kamishiro, a highschool student with a height complex, is working hard to rebuild his father's rundown kendo dojo. Then all of a sudden one day a long-haired boy in a bizarre outfit appears in front of Ritsu and says "I'm an oni! I've come to retrieve the Mallet of Fortune from you, the descendant of Issun-Boushi!" (Source: Julian Publishing, translated)