High schooler Sasae Hatsushima has been summoned to a world of dark fantasy to defeat an undead army. That shouldn't be hard when he has the help of his hyper-competent stepmom and her two younger daughters, a high school karate champion and a girl genius! But to gain the powers needed for their quest, a great and painful price must be paid... And who better to pay it than Sasae, who seems utterly ordinary compared to his brilliant stepfamily?