In Shinjuku ward's east side lies Kabukichou, a vibrant city of chaos that glows brilliantly with neon lights but also hides unseen darkness. Employed at a university hospital on the west side, John H. Watson is looking for someone who can assist him with an odd case. His search leads him to the Pipe Cat, an underground bar that serves as a meetup venue and job board for some of the best detectives in Shinjuku, the most prominent among them being Sherlock Holmes. Upon finding the bar and meeting the peculiar investigators, John learns that they are pursuing a case involving Jack the Ripper, an infamous serial killer. Due to subsequent events, John ends up driving Sherlock to the crime scene of a murder supposedly carried out by Jack the Ripper. Even though John is only there to enlist Sherlock's help with his case, he witnesses Sherlock brilliantly uncover the truth behind the crime scene. However, he begins to realize that Sherlock is not only a genius detective but also an eccentric character. As John continues to request Sherlock to assist him with his case, he finds himself spiraling into the detective lifestyle of solving cases beyond the minds of ordinary civilians. Through this work, John begins to see the true colors of the chaotic city that is Kabukichou and starts to unravel the unsettling mystery behind his own case.

For as long as he can remember, Minoru Kagenou has been fixated on becoming as strong as possible, which has led him to undertake all kinds of rigorous training. This wish, however, does not stem from a desire to be recognized by others; rather, Minoru does everything he can to blend in with the crowd. So, while pretending to be a completely average student during the day, he arms himself with a crowbar and ruthlessly thrashes local biker gangs at night. Yet when Minoru finds himself in a truck accident, his ambitions seemingly come to a sudden end. In his final moments, he laments his powerlessness—no matter how much he trained, there was nothing he could do to overcome his human limitations. But instead of dying, Minoru reawakens as Cid, the second child of the noble Kagenou family, in another world—one where magic is commonplace. With the power he so desired finally within his grasp, he dons the moniker Shadow and establishes Shadow Garden: a group whose sole purpose is to combat the enigmatic Cult of Diablos, an organization born from Cid's imagination. However, as Shadow Garden grows in both membership and influence, it becomes increasingly apparent that the Cult of Diablos is not as fictional as Cid had intended.

Kagemori Mamoru is a dowdy boy whose hair is disheveled and who wears thick glasses, but he is actually the son of a ninja family. They have protected their neighbors, the Konnyaku family, secretly for 400 years. Mamoru has personally protected their daughter, Konnyaku Yuuna, since they were in kindergarten. When Yuuna is in trouble, Mamoru puts on ninja suit and turns into a competent ninja to help her.