Naritaverse

The Naritaverse is the unofficial name for the universe in which Baccano! is set alongside five other works by Ryohgo Narita as of 2021: his light novel series Durarara!!, Vamp!, and Etsusa Bridge; his novel Wednesdays Smiling with Otsuberu, and his serial fiction Pandora Shark.

Durarara!!
Set in Tokyo's Ikebukuro district in the early 2000s, Durarara!! follows the stories of many characters and gangs of varyingly dangerous and eccentric personalities as they co-mingle and cause chaos together. Some of these individuals and groups include: a dullahan courier; a manipulative information broker; the strongest man in Ikebukuro; the Russian Mafia; the internet-based group Dollars; the Yellow Scarves gang; and an underground doctor.

Aside from Baccano!, Durarara!! (illustrated by Suzuhito Yasuda) is the only other one of Narita's light novel series to have received an anime adaptation. The anime adapts all thirteen volumes of the main series: Season 1 adapts Volumes 1–3, and Season 2 adapts Volumes 4–13. The sequel light novel series and the spin-off novels have not been animated.

Vamp!
Also set in the early 2000s (2004/2005), Vamp! takes place on the fictional island Growerth off the coast of Northern Germany and tells the story of humans, vampires, werewolves, and other supernatural creatures with imaginative zeal. Especially of interest are the vampire twins who live in Waldstein Castle along with their adoptive father and other supernatural creatures, a dhampyr mayor with a petty personality, the odd beings known as Eaters and the large and colorful cast of vampires who make up the Organization...

Vamp! has been on hiatus since the fifth light novel volume was published in 2010 due to poor sales. Its story remains incomplete.

Etsusa Bridge
Set in the late 2010s (2014; 2019–2021), Etsusa Bridge is a light novel series that revolves around a gigantic, incomplete bridge connecting the Sado and Niigata islands and the nameless artificial floating city at its center. The city and bridge have become a haven for criminals, outcasts, and mafia outfits to make a dangerous life for themselves.

Wednesdays Smiling with Otsuberu
Set during the year and a half interim between the events of Durarara!! and Durarara!!SH, Wednesdays Smiling with Otsuberu (オツベルと笑う水曜日) follows two employees of the Last Week Weekly tabloid's Tokyo editorial department—Rui Otonobe, editor-in-chief, and Yukihiro Kisa, department newcomer—as they are caught up in a serial murder case.

Pandora Shark
Set circa 2034, Pandora Shark primarily takes place on Ryūgū (龍宮, lit. dragon palace), a mobile maritime research [city / facility] built a decade after the monster 'Cannibal Shark Void' (人食い絞ヴォイド) claimed 248 lives. Of Ryūgū manifold research laboratories. one contains a terrible secret around which unfold dangerous events that involve the likes of mercenaries, local researchers, a Nebula curator, the city's mayor / facility's director, and innocent visitors.

Pandora Shark is a work of serial fiction that Narita began releasing in installments in April 2021. That month, on April 24, 2021, Narita made reference to the serial's site's description of the Nebula curator (Wilson Yamada) and confirmed that the serial's setting is the same as Nebula's origin.

Light Novels

 * In the short story Narita wrote for the 'special favor' book accompanying the game Dengeki Gakuen RPG: Cross of Venus, Ronny Schiatto has an encounter with the dullahan Celty Sturluson. Although Celty appears not to 'know of' Ronny, Ronny 'knows of' her.
 * It is possible that Dalton Strauss has seen Celty in person, since in 1935-B Dr. Feelgreed he recalls that he once saw a whole cavalry of headless warriors in Ireland. At the very least, the line is a homage to Durarara!! 's main heroine.
 * The Unnamed Photographer who narrates The Rolling Bootlegs lives next door to high school student Mikado Ryugamine in Ikebukuro, as mentioned in Durarara!! Volume 1, Chapter 8.
 * In August 2002, per Baccano! Volume 13, SAMPLE leader Bride prepares to visit "Orihara" in order to return a church key and thank him for offering to take care of corpse disposal at no cost. This 'Orihara' is one Izaya Orihara, an information broker based in Shinjuku.
 * While on vacation in Ikebukuro during July–August 2002, Nile encounters and fights Shizuo Heiwajima with Elmer C. Albatross as an eyewitness. Shizuo emerges the victor, much to Nile's humiliation. Elmer recalls the fistfight in Chapter 4 of Baccano! Volume 13, and Shizuo refers to the fight in the first chapter of Durarara! Volume 5.
 * On page 36 of Durarara!! Volume 5, Chikage Rokujou remarks, "Well, the other day I saw a thing on TV about a nobleman who loved, like, thirty different maids..." This may be a reference to Baccano! character Count Esperanza C. Boroñal, who did employ over thirty maids during his residency as Lotto Valentino's acting governor. Both characters have unique perspectives when it comes to women.
 * American filmmaker John Drox has hired actor Kasuka Heiwajima for several of his movies. Volume 4 of Durarara!! specifically mentions that John Drox tagged Kasuka as the lead for his pet project Cruiserfield, to be filmed in Japan during the springtime.
 * Volume 4 also compares the serial killer Hollywood, who wears various monster costumes as disguises while committing murder, to Isaac & Miria...who wear a variety of costumes as disguises while committing robberies.
 * Volume 4 further shows that the 'McDannell' Company—the major movie distributor behind the Shark Flight film the Walken siblings are promoting in Baccano! 's 2002 arc—has connections to the American-based talent agency Jack-o'-Lantern. Max Sandshelt presides over the Japanese branch of this agency in Durarara!!.
 * Although Durarara!! Volume 4 spells this company's name as 'McDonnell', both Volume 12 and Volume 13 of Baccano! spell the movie distributor's name as 'McDannell Company'. Victor Talbot in Volume 13 even explicitly distinguishes the movie distributor 'McDannell Company' from the aircraft corporation 'McDonnell'. Therefore, the two series' official translations contradict each other.
 * In Volume 8 of Durarara!!, Saki remarks that Charon Walken and Kasuka are strikingly similar to one another.
 * In Durarara!! Volume 11, Nebula employee Shingen Kishitani tweets that a Nebula division is researching the "liquor of immortality." He is referring to Nebula's ongoing research into the Cure-All Elixir in America.
 * From A Standing Ovation with Orihara Izaya:
 * Chapter 2: Yuuki Usubara recounts a story she heard from an American couple touring Japan that were probably Isaac and Miria.
 * Chapter 3: Two characters recall a famous American serial killer called Ice Pick Thompson, whose true identity was never discovered. Ice Pick Thompson is the subject of the sixteenth Baccano! light novel 1932 Summer: Man in the Killer.
 * Chapter 4: Izaya refers to the "influential American Runorata Family mafia" while in conversation, therefore indicating that the Runorata syndicate survives in the early twenty-first century.
 * In Durarara!! SH Volume 4, Chapter 3, a story is told of an American couple who dated for fifty years before finally getting married, and would eventually go on their honeymoon twenty years later. This is likely a reference to Firo and Ennis Prochainezo, who met in 1930 AD, married c. 1980 AD, and went on their honeymoon in 2002 AD.
 * Later in the same chapter, it is stated that Byakuyamaru Natsugawara had made contact with both the Runorata and the Russo mafia families. This may be evidence that Ricardo Russo was successful in rebuilding the Russo Family.

Anime

 * In Episode 11 of Season One, Isaac and Miria cameo as members of the Dollars in Ikebukuro.
 * In Episode 12.5 of Season One, Isaac and Miria discuss what they believe to be hitodama (or 'ghostly fireballs') spotted in the night sky. In truth, the hitodama are glow paint-covered people whom Shizuo had hurled into the air.
 * Throughout the Durarara!! anime adaptation, clips from Baccano! 's 2007 anime adaptation play on outdoor screens in the city (near the movie theatre especially), and posters featuring Baccano! characters can also be spotted throughout the anime. These are actually promotional materials for an upcoming film by John Drox based off the recently declassified Flying Pussyfoot incident of December 30–31, 1931 (the declassified information, however, is an edited version of the true events).
 * In Episode 11 of Durarara!! x2 Ketsu, Mikado mentions that his fist-gun is a weapon that a "terrorist in America" designed many years ago. The terrorist in question is one Huey Laforet, and the gun is an improved version of the hand-firing mechanism that Goose Perkins uses aboard the Flying Pussyfoot. The episode's information is derived from Durarara!! Volume 13.
 * Throughout the anime, Mikado's password for the Dollars' website is 'baccano'.

Baccano! and Vamp!

 * Carnald Strassburg (a famous historical figure from Growerth) is credited by Carla Alvarez Santoña in 1711: Whitesmile as the engineer who designed House Dormentaire's floating barricade of ships stationed in Lotto Valentino's harbor by 1711. In the same novel, Lucrezia de Dormentaire remarks that Strassburg was also responsible for Growerth's perfect sewage facilities.
 * Several of his paintings also hang in Nebula's headquarters in Chicago in 1934, the bronze statue outside of which is additionally his design and cast. Gustav St. Germain comments that Nebula seems to besotted with Strassburg's work.
 * The Advena Avis is procured at a great debt by Dalton Strauss from the Mars Clan, a vampire clan that was powerful and teeming with members at the time. By the early 2000s, the Mars Family has lost all its members save for its leader, Romy Mars, who may have been alive during the time of the 1700s arcs.
 * According to Claire Stanfield, one of his colleagues back in the circus was a self-professed vampire who could perform such tricks as turning his hat into a flock of bats. The vampire's shining suit, coupled with the specific mention of his name by Charkie in 1935-D: Luckstreet Boys, pinpoint him as Doubs Hewley, a vampire from Vamp!.
 * In Vamp! IV, vampire Rude Gardastance contemplates the Nebula owned "Mist Babel" skyscraper in Chicago from his penthouse in the early 2000s. He also mentions that he has a debt to Nebula's chairman from five generations ago; it is possible that this chairman is Cal Muybridge.
 * Rude is also referenced in 1934 Peter Pan in Chains: Finale, when Chairman Muybridge remarks that Ladd Russo should have gone to "Rude, Beriam, or one of those other fellows with money" if he wanted to cause trouble for Nebula back when he was a youngster.
 * False Ending 21 of the Baccano! NDS Game essentially serves as an advertisement for Vamp!. It features Isaac and Miria aboard the Flying Pussyfoot, where they come across a moving mass of red liquid which forms itself into letters. Convinced that there is an invisible man vampire in the train, Isaac and Miria flee. The mass of blood is actually the vampire Gerhardt von Waldstein.
 * In 1705 The Ironic Light Orchestra, the Third Library is said to have been built "with financial backing from the ancestors of a noble family on an island in the north of Prussia," and that the family had continued its support since. This is affirmed again in 1710 Crack Flag, which states the Third Library is said to be funded by a "nobleman from an island in northern Prussia." This island is Growerth, the main setting of Vamp!
 * In 1935-B Dr. Feelgreed, Dalton recalls in 2003 that he has "seen werewolves and vampires on an island to the north." This island must be Growerth; when Dalton visited Growerth is unknown.

Baccano! and Etsusa Bridge

 * In Volume 3 of Etsusa Bridge, serial killer Yakumo Amagiri mentions having heard of a female assassin in the United States who fought with two katanas. He is thinking of Maria Barcelito.
 * "In Baccano! Volume 7, Christopher Shaldred claims he committed a massacre because "a flower was pretty," and later falsely says he wants to kill Claire "because the rain is noisy." This is the logic Yakumo uses during his reign as a serial killer approaching a century later.
 * Baccano! character Angelo states that he has a son called Carlos (who turns three in 2002) whom he has not yet met. Angelo is a Spaniard, an excellent sniper/gunman, and wears blue shades. One of Etsusa Bridge 's characters in 2019 is young man called Carlos who is also Spanish, an excellent sniper/gunman, and wears blue shades. It is likely that these two Carloses are in fact the same person.

Note that the powerful Nebula corporation is referenced across all series, or at least, all save Otsuberu. Its influence is especially significant in Durarara!! and Baccano!.

Baccano! and Wednesdays Smiling with Otsuberu

 * A still image of Isaac and Miria—taken from Episode 16—appears on the front cover of Wednesdays Smiling with Otsuberu. A red marker heart is overlaid over their 'photograph', which is titled 激写 ("A photo taken at a sensual/at just the right moment"). Isaac's face is covered by the novel's title on the front cover, but is fully visible on the inside cover.
 * In Wednesdays Smiling with Otsuberu, an article in the Weekly Fly High magazine mentions something about an 'immortal human' in the New York mafia. The Last Week Weekly employees reading the article wonder if this is the same person in some photographs from 1930 and 2002, one commenting that it should be 'Camorra' and not 'mafia'; in light of this, the 'immortal human' in the article may be a member of the Martillo Family.