The story takes place in a fictional city called Hersharemz Loth. The distortion of time and space has connected the other world and the human world. As a result, the ancient race "Blood Boundary Family" living in the other world has descended, posing a great threat to human safety. In order to maintain world peace, a secret organization called "Secret Society Libra" is actively operating in secret. Leo (voiced by Daisuke Sakaguchi) was originally an ordinary boy. By chance, he accidentally joined Libra and became a part of punishing evil. Then he met Klaus (voiced by Rikiya Koyama), who is rough in appearance and gentle in heart, Zap (voiced by Kazuya Nakai), who is cheerful and glib, and Qian Huang (voiced by Yu Kobayashi), who looks ordinary but is actually a werewolf. These like-minded friends opened a different prelude to Leo's life.