The hero, Haishen Hang, is a callous boy who only strives for his studies. The story begins in the bustling Tokyo. It is the day when the exam results are released. Hang and his classmate and friend Chan-o go to see the results. He thinks that victory is a matter of course, but he finds that his number is not on the list! It turns out that he chose the wrong answer to the multiple-choice question. So he failed the school entrance exam, and the housekeeper who has been taking care of Hang is also leaving him! Just when things are getting so bad, two mysterious people suddenly appear and say congratulations to Hang for being recommended to study in a mysterious school, and the school is on a mysterious island - Promised Island... Hang was very reluctant at first, but because he had no choice, he had to set off. When he arrived on the island, he found that everything was weird. In addition to constantly seeing old people who looked like housekeepers, appearing around Hang in different roles, the most shocking thing was that twelve beautiful and lovely girls appeared one after another, and they also claimed to be Hang's sisters! That's how Hang lives on this island with twelve sisters with different personalities, opening the most gorgeous chapter in his life...At the same time, another girl named Zhen Shen, pretending to be Hang's thirteenth sister, sneaks into Welcome House and lives with Hang and his sisters in order to monitor his every move. She also often communicates with a mysterious person via email, whose goal is to get little Hang to return to hopeless Tokyo.