Linebarrels of Iron (2008)

Kouichi dreams of being a hero, but in reality, he's a punching bag for every bully on the block. His life flatlines when the mysteriously naked Emi crash lands on his pitiful existence, thrusting Kouichi into the middle of an intergalactic showdown between rival races of self-regenerating Machinas. Through his death-bed partnership with the Linebarrel mecha, Kouichi gains the strength to stand up to his tormentors and crush the alien invasion force that's determined to conquer Earth. There's just one problem. All this newfound power and special attention from nearly-naked babes is turning Kouichi into a jerk. His friends can't stand him, he makes his dream girl sick, and those aliens want to kill him extra dead! Kouichi may have the mechanized muscle to save the world, but he has much to learn about being a true "Hero of Justice".