The hugely popular light novel series by nigozyu, which has surpassed 1.8 million copies in worldwide circulation, returns with its long-awaited second anime season. Regular Edition Blu-ray Volume 1 is released. The accomplished staff behind the high-quality first season, which drew attention for its dynamic action scenes, return, including director Manabu Kurihara, character designer Yosuke Ito, series composition writer Deko Akao, and animation studio ENGI. "Will you be my assistant?" Kimihiko Kimizuka, a boy with a tendency to get caught up in trouble, became the assistant to Siesta, a girl known as the Great Detective who fought the Enemies of the World aboard an airplane flying 10,000 meters above the ground. The two traveled around the world for three years and experienced a series of dazzling adventures before they were separated by death after a fierce battle. One year after Siesta's death, Nagisa Natsunagi appears before Kimizuka, the sole survivor, claiming to be a client. Kimizuka becomes an assistant once again after accepting her request and eventually reaches the truth behind the Great Detective's death. However, as they confront that truth, Kimizuka and the others learn about the mistake made by the infallible Great Detective and the true meaning of carrying on her will. The detective is already dead. The truth behind her death has been revealed, but it is still too early for the epilogue. Includes episodes one-five. [Bonus footage] Non-credit opening