The dangerous imitation tonic hits the market, spreading unprecedented mayhem throughout Natsukibara. Getsu and Reiji have been working hard to track down the mastermind behind the recent series of terrible events. But then, like a punch to the gut, their boss at Fantastic Sweeper orders them to halt their investigation! Though the boys don't want to comply, there is not much they can do when Beast Tech Headquarters gives the order. However, when news breaks that the CEO of Beast Tech is on their deathbed, desperation mounts. The CEO is the only one who knows the base recipe for the Monster Tonic, so the most likely successor is...Kei! The CEO's death could prompt magic users around the world to clash, bringing about the most horrific Walpurgisnacht. Will Getsu and Reiji be able to keep their friends safe?
