Wataru Minakami, a stellar student, faces a setback when a computer error derails his high school entrance exam results. Unexpectedly accepted into Stargazer Hill Academy on the enigmatic Promised Island, Wataru is urged by his father to journey there. Upon arrival, a bevy of endearing girls approach him, asserting they are his younger sisters. Delving into the bond with his alleged siblings reveals a compelling enigma surrounding their shared exile to the island.