The “Seven Deadly Sins”—a group of evil knights who conspired to overthrow the kingdom of Britannia—were said to have been eradicated by the Holy Knights, although some claim that they still live. Ten years later, the Holy Knights have staged a Coup d'état and assassinated the king, becoming the new, tyrannical rulers of the kingdom. Elizabeth, the king's only daughter, sets out on a journey to find the “Seven Deadly Sins,” and to enlist their help in taking back the kingdom.

Mikado Ryugamine moves to Ikebukuro at his friend’s invitation and quickly becomes entangled in the city’s dangerous underworld. After witnessing the legendary Headless Rider, he finds himself caught up in escalating violence and gang conflict that begin to throw Ikebukuro into chaos.