This world is heavily ruled based on the amount of "sins" each person carries. At the age of 10, they are tested. With 1 sins, they are high class, with 6, they are the lowest class. Those with 0 sins are called saints and those with 7 sins are viewed as the devil incarnate, eliminated immediately. However, as time progress, the society gave those with 7 sins a chance. Aki, a 7 sins carrier, is given a chance to study in the top society High school among 1-2 sins people and the one and only saint. Aki has to prove to have the quality to change before graduation or else she will be taken. During this time, she will meet with someone who will grants her the happiest time of her life.