In the detective business, everyone knows the name Keiichirou Nagumo. Back in high school, he was called a genius for cracking tough cases that even the police could not solve. But those days are long gone—or so the rumors say. However, one day, an unexpected visitor barges into his office: Mashiro, an energetic high school student who demands to be hired as his new assistant. Although Keiichirou tries to brush her off, Mashiro is persistent. She is determined to become a detective, and to prove her worth, she begins by teaching him about the latest technology and offers a fresh perspective on his business. Thus, Keiichirou takes Mashiro on as his assistant and embarks on a brand new chapter in his career—one where he finds himself constantly surprised by the modern generation of detectives.

Mogura, a mysterious "self-proclaimed sage" also known as Hyakuan Momoyumi, has been banned from the afterlife. To return, he roams the world, collecting the "lamps" of ghosts in his lantern. However, crossing paths with him brings an unusual consequence: the ability to see strange phenomena...

Despite being one of the most promising candidates, Allen fails the final exam for the position of royal court sorcerer, forcing him to abandon his ambitions and return home. Adding to his woes, he does not even have enough money for the train fare back, stranding him. With help from a former professor, Allen secures an unusual job offer: to be the private tutor of the daughter of Duke Howard, one of the kingdom's most powerful nobles. The girl, Tina, however, has one critical flaw—she is completely unable to use magic. Though her academic prowess is nothing short of prodigious, intellect alone is not enough for the fast-approaching entrance exams to the prestigious Royal Academy. Moreover, countless magic instructors have tried to solve her problem and gave up in the process. To help Tina overcome her limitations, Allen must dig deeper into the roots of her magical inability, and, in doing so, uncover far more than he ever signed up for.

Toto has been dreaming about adventuring with other people for as long as he can remember. Despite his hero title, he still remains without allies due to his timid personality. Therefore, when three women: Ciel, Anemone, and Goa suddenly request to join him, Toto is overjoyed. Unbeknownst to him, they are all assassins assigned to eliminate him! While Toto resolves to protect his would-be killers, the women fight over who can finish off the hero. As Toto remains oblivious of his new party members' true intentions and finds himself passing out every time he gets flustered, the four of them embark on their peculiar adventure into the greater world.