Just before summer break, high school sophomore Manatsu Daichi spots an odd, circular rainbow hovering in the sky above Tanegashima. Driven by a sense of familiarity, he journeys there solo, despite being haunted by traumatic memories of his late father's enigmatic demise, as well as a perplexing interaction with a peculiar boy and girl. Upon arrival, Daiji hears the blaring warning of an establishment named "Earth Engine," and is promptly questioned if he is the captain. Seconds later, invaders from Uranus known as "Kill-T-Gang" swoop in, setting the stage for a fierce conflict over the twinkling cosmos.