Naota Nandaba is a regular sixth-grader living in a city where nothing extraordinary ever appears to happen. After his brother Tasuku leaves town to play baseball in America, Naota takes on the responsibility of looking after everything Tasuku left behind, including his ex-girlfriend Mamimi Samejima, who hasn't stopped clinging to Naota since Tasuku departed. Naota has no idea that his humdrum existence is about to alter forever: enter Haruko Haruhara, a Vespa-riding, bass guitar-wielding, pink-haired maniac whose first meeting with Naota leaves him with tire marks on his back and a big horn on his head. Even though all he wants is some peace and quiet, when Haruko moves in with his parents, Naota discovers himself dragged into the heart of the greatest battle for supremacy that Earth—and quite possibly the entire universe—has ever seen.