Welcome to the quaint seaside village of Uchioi, home to fishing, festivals… and the Gyuuki, an ancient demon sealed away beneath the waves centuries ago. All that’s about to change, however, as the Gyuuki shows signs of reawakening. The fate of Uchioi now rests in the hands of one teenage boy: Mamoru, called back to the Minami family seat by a distant relative. He now has only four days to defeat the Gyuuki… and they’ll prove to be the longest four days of his life.