Durarara!!x4 (デュラララ!!x4) is the fourth light novel in the series. It contains the series' fourth story arc, the Hollywood Arc, and was adapted into volumes 13-14 of the manga and the first part of Durarara!!x2 Shou, the first cour of the second season of the anime.
Ikebukuro is on holiday and all of its residents and visitors are ready to make the most of it. Twins who are the perfect opposite of each other, an idol nothing like his older brother, new high school students, returning high school students, yakuza executives, an underground doctor, a movie costume-clad serial killer, a legendary Russian assassin, a Headless Rider with a bounty on her head. The neighborhood is full of fires waiting to be lit and plenty of people ready to light a match.