Ataru Moroboshi and his classmates at Tomobiki High are gearing up for their school festival when the day refuses to end, the same morning looping no matter what they do. Investigating with Lum and Shuutarou Mendou, they discover the entire town now floats on a giant turtle adrift in a decaying dreamscape shaped by a hidden demon. Ataru has to find a way out of the endless festival-eve loop before the dream swallows them all.