Baccano!

In 1711, a group of alchemists seeking eternal life gathered on a boat to summon the "demon" that held the secret. The demon agreed to give them what they wanted—an elixir of life, the method to create more, and the secret to ending their new-found existence. The following night, alchemists began disappearing, "eaten" by one of their own. Realizing the threat being close together posed, they decided to scatter across the world. Centuries later, in Prohibition-era America, the immortals have come together once again, and the "stupid commotion" (baccano) starts.

New York, 1927.
In a corrupt city where crime rules the streets, Firo Prochainezo is in the Camorra, an Italian criminal syndicate distinct from the mafia. Though a member of the relatively small Martillo family, Firo has big ambitions and is determined to make his mark. But while the Martillos may not be the biggest bad guys on the block, they've got some distinct advantages working in their favor. Does Firo have what it takes to become a made man?
Let the crazy ruckus begin!
(Source: Yen Press)

In 1705, a rash of murders takes place in Lotto Valentino, a provincial city on the Italian peninsula. The murderer, who wears a pure white mask and places one such mask on all of their victims, is known as the "Mask Maker," and anyone who witnesses their murders becomes their next victim. Huey Laforet, a boy who attends a "private school" for alchemy, hates everything about the world. Monica Campanella, his schoolmate, confesses her feelings for him. Elmer C. Albatross arrives in town as the school's newest student. Niki, a merchant's slave girl, witnesses one of the Mask Maker's crimes. All four youths must confront the Mask Maker and a conspiracy to control the entire city — the start of a 300-year-long struggle amongst immortals.

Set on a giant, almost finished bridge between Sadogashima and Niigata. Abandoned by the government, the bridge, and the giant man-made floating island at the center, has become a city of criminals and societal drop-outs. 

Set in the same world as Durarara, but 15-20 years later. There is almost no overlap between Etsusa Bridge and the other novels.

THE GOOD, THE BAD, AND THE DOWNRIGHT WEIRD.The Ikebukuro district in Tokyo is full of interesting people. A boy longing for the extraordinary. A hotheaded punk. An airheaded pseudo-stalker. An information broker who works for kicks. An underground doctor who specializes in truly desperate patients. A high school student infatuated with a monster. And a headless rider on a pitch-black motorcycle. Their story may not be a heartwarming one, but as it turns out, even weirdos like these sometimes fall in love.(Source: Yen Press)

A comedic dark fantasy about vampire clans, a vampire princess, and the man who hunts them!
"Dear ladies and gentlemen of Japan! I apologize for asking such a mundane question, but do you all believe in vampires?"
"I beg your pardon. It seems I'm a bit tardy in identifying myself. My name is Gerhard Von Balstein. I am a vampire, entrusted with the Island of Growerth and bestowed with the title of 'viscount.' Instead of introducing myself, I thought I might recount the story of a disturbance which occurred on my island. Or might I say, please allow me to tell you since I have some time on my hands."
"Whether you believe my story or not, I'm sure it is as clear as daylight that I am not a person. At any rate, my body is..."

(Source: Seven Seas Entertainment)

A girl with bloody iron pipes, sleepy eyes flickering - just talk.
"On the Islands, a gunshot echoes today. As usual. People die. As usual. Dogs and more dogs, the dogs, well, kill each other. As usual. The Bosses of the eastern sections, transform. As usual. A fellow murderer, using swords and the eastern sections of the cat, the brother Li Feng, the detective brother, cute guys, clumsy love. As usual. The Island, I'm terribly confused. ... as always. After all, as usual. The island today is As Usual. That's it. So I, as always, the cute child, hug a lot. It's warm. I'm... sleepy"
A series of short stories set on Etsusa Bridge.