After a mysterious shortage in guardian angels, God decides to send their most trusted angel, a Cherub named Sincerity down to protect a reckless human, Autumn. Autumn, with no sense of danger, decides to make a blood contract with a succubus named Valentine that is obligated to stay by her side until her soul depletes of its magic. Without God's direct aid, Sincerity is forced to tolerate the presence of Valentine, figure out what is causing the guardian angel shortage, and protect Autumn.
