In a world where humanity fights against demonic incursions from the demon realm, two girls, the fox-spirit Shenfu and Lisa, who made a master-servant contract with her during their very first meeting, causing her to stop ageing, are on a very yuri journey to defeat these monsters wherever they might appear. But there is a certain _secret_ to their power in battle... While Shenfu's spirit magic allows them to increase both their physical and mental strength, their relationship slowly starts becoming not just purely physical, but something deeper... Just how will the monster-exterminating yuri journey of the tsundere girl who can't be honest with herself and her very affectionate fox girl "servant" end...?