In Tokyo's downtown district of Ikebukuro, amidst many strange rumors and warnings of anonymous gangs and dangerous occupants, one urban legend stands out above the rest—the existence of a headless "Black Rider" who is said to be seen driving a jet-black motorcycle through the city streets. Mikado Ryuugamine has always longed for the excitement of the city life, and an invitation from a childhood friend convinces him to move to Tokyo. Witnessing the Black Rider on his first day in the city, his wishes already seem to have been granted. But as supernatural events begin to occur, ordinary citizens like himself, along with Ikebukuro's most colorful inhabitants, are mixed up in the commotion breaking out in their city.

Based on a series of light novels written by Tanaka Yoshiki and illustrated by Kakinouchi Narumi. The story revolves around Ryouko Yakushiji, a 27-year-old multilingual investigator that graduated from Tokyo University's elite Department of Law, and the bizarre cases she faces while working for the Tokyo Metropolitan Police. Yakushiji not only has to deal with supernatural beings in her line of work, but also her rival Yukiko Muromachi, another equally talented and beautiful police investigator.

A normal looking high school girl on the outside, Kusakabe Maron is actually the reincarnation of Jeanne d' Arc. With the help of the angel, Fin Fish, Maron works as the thief Jeanne at night to seal the demons that reside in pieces of artwork, preying upon the weak hearts of the owners. She is branded as a thief due to the fact that the artworks disappear after she seals the demons. One day, a new neighbor and classmate appears, as well as a rival in her night job, the thief Sinbad. With her own best friend being the detective's daughter, out to capture her and the appearance of her new rival, Maron's work is anything but easy.

Tricked into assassinating his own prospective father-in-law, righteous samurai Raizou Kurima is overwhelmed with guilt. In order to reclaim his honor, Raizou swears vengeance on the lord who gave him those misleading orders. In his pursuit, he is aided by self-proclaimed merchant-of-all-trades Yuuen Usui, who is actually one of the Revengers—assassins who seek justice for the wronged and dispense bloody revenge on their behalf. Tragedy seems destined to follow Raizou as he becomes increasingly intertwined with members of the Revengers. As he begins working as a vigilante alongside them, the complicated web between the corrupt Japanese political elite, the unscrupulous Europeans, and the Revengers gradually reveals itself. The more entangled he becomes in these affairs, the more Raizou realizes that justice is as deceptive as the honor that he sought to redeem.