Shinjuku

Shinjuku is a city ward in Tokyo and one of the capital's major commercial centers. It lies to the south of Ikebukuro, and several railway lines connect the two. Shinjuku houses a skyscraper district built of offices and upscale restaurants and hotels, a large urban park, and one of Tokyo's busiest entertainment and shopping areas that includes the city's redlight district. The Awakusu-Kai have offices in Shinjuku, and it has been Izaya Orihara's home since he fled Ikebukuro prior to the start of the series.

Izaya's apartment/office
Since being forced out of Ikebukuro prior to the story's start, Izaya has been living and receiving clients in his apartment in Shinjuku. His apartment is exceedingly spacious by Japanese standards. After the events of the Dollars/Mika Harima arc, Namie Yagiri has been working in his office as his secretary.

Awakusu-Kai offices
The yakuza syndicate has members working in several different parts of Tokyo. On a visit to Shinjuku in search of Izaya, Shizuo Heiwajima is framed for the brutal murder of several Awakusu-Kai subordinates after discovering the bodies of several members in one of the group's offices.