Due to a computer glitch, Wataru Minakami, a top student, failed his high school entrance exam. However, he found solace in being accepted to Stargazer Hill Academy, situated on an enigmatic location known as Promised Island. Wataru's father requested that he be transported to the island where several lovely and endearing girls promptly came to claim him as their elder brother. As Wataru adjusts to his unique situation, a more profound enigma arises: the purpose behind his siblings' presence on the isolated island.