Amagi Brilliant Park: Volume 1 by Shouji Gatou

Amusement parks are places of wonder and fun for all ages... right? Well, that's not quite the case for Amagi Brilliant Park, a "crummy" amusement park on the outskirts of Tokyo where the snacks are inedible, the attractions are falling apart, and the mascots regularly get into fistfights with the guests. It's the kind of place that cool, handsome, brilliant Kanie Seiya wouldn't be caught dead in... until a mysterious girl drags him there--at literal gunpoint--and demands that he help them save the park!

From the author of Full Metal Panic!