Durarara!! (デュラララ!!), shortened to DRRR!! in some official materials, is a Japanese light novel series written by Ryohgo Narita, with illustrations by Suzuhito Yasuda. Durarara!! tells the story of a dullahan working as an underworld courier in Ikebukuro, an internet-based anonymous gang called the Dollars, and the chaos that unfolds around the most dangerous people in Ikebukuro. The series ran for thirteen volumes, published by ASCII Media Works under their Dengeki Bunko imprint. A sequel series, titled Durarara!! SH set two years after the events of the original series, started in 2014.

Yozakura Quartet is a Japanese manga series written and illustrated by Suzuhito Yasuda. It has been serialized in Kodansha's shōnen manga magazine Monthly Shōnen Sirius since January 2006, with its chapters collected in 30 tankōbon volumes as of December 2022. In North America, the manga was first licensed by Del Rey Manga, and later by Kodansha USA for a digital-only release.