Naritaverse

The "Naritaverse" is the unofficial fan name given to the shared univese that was created by Durarara's author, Ryogo Narita. The Naritaverse encapsulates ''Durarara!! along with 3 other novel series Baccano!, Vamp!, and Etsusa Bridge''. This page is dedicated to listing Durarara's connections in all three mediums: Anime, Light Novel, and Manga, to each of these series.

Please note that due to the relative scarcity of info on Narita's novels outside of Japan, much of this information is subject to change as new facts come to light.

Timeline & Brief Summaries
Due to the overlapping and somewhat chaotic nature of Narita's storytelling, an exact timeline is difficult to place for the Naritaverse. However, we can give you a rough estimation of when each series takes place to give a better understanding of how they all relate to each other.

Baccano!
The earliest entry in the Naritaverse. Baccano tells the stories of various immortal beings and the chaos they bring to themselves and those around them. Stories in this series take place in a variety of different time periods from the early middle-ages to the prohibitian era of the United States and more recently in the early 2000s.

Vamp!
Taking place in modern day Germany, at around the same time as Durarara's storyline, Vamp! tells the story of 2 vampire twins with unique properties, their adopted father, and many other vampires, humans, and variations of the two that get dragged into their story.

Etsusa Bridge
The latest entry in the Naritaverse, Etsusa Bridge is set approximately 10 years after the end of Durarara's first series of novels and takes place in a city built on a man-made island that is located in the center of a massive bridge between Sadogashima and Niigata. The Bridge, and by extension the city has been abandoned by the world at large and has become a haven for out-laws and outcasts.

Yozakura Quartet
The story of a strange city called Sakruashin Town which is populated by both demons and humans. Stories typically center around the demons and humans attempting to coexist peacefully with each other while a terrorist plots to merge the demon and human worlds together. While not officially considered part of the Naritaverse, at least one reference to Sakurashin Town is made which implies that Durarara and Yozakura Quartet are related.

Anime

 * Isaac Dian and Miria Harvent, a pair of eccentric immortals from Baccano, are present at the first Dollars meeting in Ikebukuro. (Episode 11)
 * Isaac and Miria are also seen discussing "Japan's ghostly fireballs" (Hitodama in the original sub), actually people covered in glow paint thrown across the sky by Shizuo. (Episode 12.5)

Light Novel

 * Nile, one of the original immortals from the Advenna Avis, somehow gets into a fight with Shizuo while on vacation in ikebukuro. The fight ends in Shizuo's favor.
 * The unnamed photographer who narrarated volume 01 of the Baccano novels apparently lives in the apartment next to Mikado.
 * Ronnie Sukiart, a high ranking member of the mafia as well as the demon who bestowed the crew of the Advenna Avis with immortality, is apparently an aquantance of Celty's. However, the details on how they met aren't known.
 * During the modern day story arc, Boss Buraido mentions "Orihara of Shinjuku" as one of his primary information sources. This is an obvious reference to Izaya.
 * Izaya also appears during the aftermath of the hijaking of the cruise ship The Entrance as it docks in Japan. Izaya assissts Buraido in disposing of the bodies of some of the hijackers.
 * In volume 08 of durarara, Saki makes a comment on how the child actor, Charon Walken, bares a striking resemblance to Kasuka. It's worth noting that Charon, along with his sister Claudia,  are the great grandchildren of Felix Walken(formerly known as Claire Stanfield) and Chane Laforet.
 * A popular director in Baccano!, John Trox, frequently hires Kasuka for his movies.

Light Novel

 * To date, Vamp! is the only series to have a full on crossover with Durarara!! Appropriately titled Duramp!, the short story follows a pair of Succubi (demons who feed off the lustful desires of men) as they journey to Ikebukuro for their next meal.
 * The first succubus visits Walker in his sleep and shapeshifts into one of his greatest fantasies, a green haired maid. The next day, Walker attempts to tell his friends about how said maid had visited him the night before but everyone else just dismisses it as his usual ramblings.
 * The second Succubus chooses Shizuo as her next target and decides to take the form of the most prominent person in his mind. Unfortunately for her, at the time, Shizuo had just gotten out of another fight with Izaya and the encounter was still fresh in his mind. Mistaking Shizuo's blind hate for blind passion, the succubus takes Izaya's form and attempts to flirt with him. Thinking Izaya had returned for round 2, Shizuo savagely beat the succubus into the ground and went home. The succubus, meanwhile, returned to her previous city horrifically traumatized.
 * A famous martial artist in Vamp!, Traugott Geissendorfer, owns a series of martial arts schools across the world Mairu Orihara learned most of her martial arts skills from the japanese branch of one of his schools before eventually moving to Rakuei Gym. On a side note, Shizuo is also a big fan of Geissendorfer.
 * A famous artist from Vamp!, Karnard Strassburg is also briefly mentioned by Shingen while solving a crossword puzzle that required the artists name for one of it's answers.
 * Also, a fake lithogragh of one of Strassburg's paintings was attempted to be sold to Chikage at an art gallery in Ikebukuro.
 * Tsukumoya Shinichi, a character who appears briefly in a handfull of durarara's novels, acts as one of Izaya's primary information suppliers. It is implied that Shinichi does not exist in the real world and only exists on the internet which makes him a sort of AI. A character in Vamp! called Husky Mouse also claims to only exists on the web and is part of a race of beings who only exist in digital form. It is likely, though not outright stated, that Tsukumoya is a member of this same race.
 * On an unrelated note, Tsukumoya is probably one of the only people that can genuinely get Izaya upset just by talking to him. This is primarily due to the fact that Tsukumoya always seems to have the upper hand on Izaya when it comes to gathering information.

Light Novel

 * It is said the Celty and Shinra have something to do with the political scandal caused by the constuction of the bridge.
 * Aoba is seen conversing with an unknown individual at varying points in the novel. This person is named Yatsufusa who is one of the main characters in Etsusa Bridge.
 * Kuzuhara Souji, the youngest son of Kinnosuke Kuzuhara, is a police officer stationed on the City built on top of Etsusa Bridge.

Yozakura Quartet

 * Kida Masaomi is seen singing Sakurashin Town's anthem in one of the chatroom conversations in Volume 04 of the light novels and directly mentions Sakurashin Town as the origin.
 * Assuming this is the same Sakurashin Town from Yozakura Quartet and due to the large demon populace of said town, this reference implies that the existence of Demons and other supernatural creatures is common knowledge in the Naritaverse.
 * If this assessment is true, a minor plot hole exists during the first dollars meeting when Celty reveals her true form. Many people were surprised or even horrified at Celty's appearance. Assuming demons are common knowledge, a headless horseman riding around a city shouldn't come as this big of a shock.
 * It is possible that Sakurashin town isn't well known to the world at large and as such, while people may know the town exists, it's large demon population could be kept secret from the general public. This would make Ikebukuro's response to Celty's nature a bit more believable.
 * Alternatively, it is possible that, while demons are confirmed to exist, they are extremely rare outside of Sakurashin Town and as such it would mean most humans have very little experience with the super natural which, again, makes the public's reaction to Celty more plausible. This also makes Celty's relatively quick acceptance into normal society more believable as, after her big reveal, all that occurs are a few news reports and an increase in police patrols. Were Celty the first supernatural creature to go public, it would have attracted much more attention than a mild increase in traffic patrols.