Underworld Fanfiction Crossover Novels & Stories

Descended from two lines of assassins, Alina Istrati is one of the most prolific assassins in the world. Always taking pride in her work, the cold nature of her crimes paired with her modus operandi earned her the alias, Blackheart. A new contract that should have been a simple job proves to be more than she bargained for when she finds herself the target of the person who hired her. On top of that, she's stuck babysitting her former target, who intrigues her at every turn. Alina will be put to the test as she fights to uncover diabolical plots and uphold obligations in the assassin underworld while trying to maintain her Blackheart status around the man she was assigned to kill. Follow ADB_Stories on IG for series updates. Codename: Blackheart is the first book in the Codename trilogy.

"But my quest is not over. For in the name of all that is evil, I promise Athena, I will be back!" The story of Medusa continues, for when she was slain, her life didn't end, for it was yet to begin. As I walked into the great room, there stood Hades, black jeans and a tee, with a hue of blue......sexy hair. This couldn't get any worse... The goddess Medusa is back and vengeance is coming upon Olympus. Athena is in for the battle of her life as Medusa has the entire nation of the underworld at her command. Medusa would reign terror down on the gods and in return for his help, Hades wants Zeus' throne...... "You wouldn't kill your own role model Medusa darling?" Athena asked, the fear evident in her voice. "You started this war, I'm just doing you a favor by ending you in it."

Milo Petrov ruled Russia’s underworld with an iron fist. For years, I was nothing more than his possession—his plaything, his captive. His wealth and dangerous charm ensnared me, but I couldn’t escape the truth: I was nothing more than a pawn in his game. At just 19 years old, I never imagined my life would spiral so far out of control. He was ruthless, but everything about him intrigued me. The only problem? I had once loved his son, Andrew. Now I found myself torn between the deadly allure of Milo and the guilt of betraying Andrew, my first love. Could blood really be thicker than desire? My name is Emilie, and this is the twist story of how Milo Petrov took my heart and shattered my world.

“Stay still, Elena.” Alessio’s voice was a dark command against her ear. His hands pinned her wrists above her head as Gabriel’s lips trailed down her throat. “You’re ours now. No running. No escape.” Two ruthless mafia kings. One woman caught between them. Elena Rossi never planned to belong to the underworld, but when she witnesses a murder, she becomes their obsession. Alessio De Luca—cold, calculating, and possessive. Gabriel Moretti—reckless, dominant, and just as deadly. Instead of silencing her, they claim her, trapping her in a world of sin, power, and raw, unrelenting passion. But the deeper she falls, the more dangerous their secrets become. And when enemies close in, Elena must decide—can she survive being theirs, or will their love ruin her forever?

Liza is a human female that has no knowledge of the dragons and wolves. She happens to be the mate to both the Dragon King and Wolf king. There was a great war between the shifters with many casualties on both sides. Both sides kept the war hidden from humans and decided it was best to never show their animal side to humans. Dragons are powerful and protected by magic. The King is a powerful CEO. Wolves are strong in numbers but since they aren’t protected by magic they won’t fight a dragon alone. Since the wolves animal forms can go undetected they’ve become the perfect assassin so they run the Underworld Mafia. Liza must decide if she wants to be the wife of a powerful dragon. Or Luna of the underground Mafia. She could also choose both. Will she be able to end the centuries long war and bring peace to the shifter community or cause another war? Who will she choose?

A new sparks ignites Alanna's boring life when she gets unceremoniously kidnapped and taken to the underworld where she meets Zeron, a demon who is the king of the ice witches. Alanna thinks she has heard it all until she discovers that the king has been terminally ill for centuries and is dangerously controlled by his darkness, as a result of a curse that had been placed on him as a child. Furthermore, Alanna finds out that she is the king's cure and in order for the king to be free from the curse, she has to bond with him in every way, including marriage. Having nothing to lose, she agrees to help the king. Soon, she's falling in love with him. But will her innocent love be enough to save him? Will her passion remain unrequited, or will she finally succeed in breaking the icy walls surrounding the demon king's cold heart?

Everything was seemingly perfect for the innocent and naïve Annalise, as she had the perfect life that any teen could ask for. With her mother, aunt, and the almighty by her side, she didn't need anyone, for she trusted them with all her heart. She was betrothed to a guy who was four years older than her but she didn't mind it one bit as it was her mother who arranged it for her and had complete faith in her mother's decision for her. But one day out, caused hell to break loose as she was spotted by the devil himself. He who ruled the underworld like the king. When his eyes landed on the sweet little teenager, he wanted her and all for himself. And what he wants he gets either by hook or crook. For he had already written his name on the innocent Annalise with his lustful eyes.

Zyran Eryx, a name that rang terror through the hearers. The most powerful Alpha King to ever exist. Rumor had it that he was blessed by the moon goddess herself and the underworld king, Hades, brother to Zeus. No one knew how he came about or anything about his family, but they've heard of the terror he brought, the horror of what he did. He is otherwise known as the Cruel Alpha King. No one crossed his path and lived to tell the tale of it, not even their soon to be dead families. He's not one to be trifled with. The only one who lived to tell the story couldn't tell it. What can a crazy man say? It was wide knowledge that the king had no heart, and is a cruel unforgiving bastard and it so happened that he's my ex's brother. One more thing, I'm his mate.

“There will be no escape for you, Regina. You belong to me now; heart, body and soul. Mine to do with as I please.” Draco’s eyes were ablaze with deadly desire. I smirked in the face of death. “Good luck with that.” ** Regina Milanesi has never backed down from a challenge no matter who stood in her way. She’s risen from her ashes and is now on her way to becoming the most ruthless woman to take the criminal underworld by surprise. But in doing so, she’s garnered the attention of Leonardo Draconis D’Angelo, the Capo dei Capi, the most ruthless and heartless man in the underworld. She loathes him with a vehemence that can only be matched with her desire to claim and be claimed by him. But her addiction to Draco just might be the beginning of her downfall, like a moth drawn to the flames…or the start of a love story written in blood.

Vivian Kane is a ghost in the digital underworld, slipping into Alessandro Costello’s world like she’s always been there. She lifts his wallet with a swipe of her fingers, and just like that, she’s not only hacked his systems—she’s hacked his life. Alessandro Costello doesn’t do forgiveness. She’s made it personal, and now he’s out for blood. He’s ready to turn her life into a living nightmare, using every dirty trick he knows to make her regret ever crossing him. What starts as a simple theft quickly spirals into something far darker. They’re trapped in a high-stakes game of cat and mouse, where every touch and taunt turns up the heat until it’s a steamy, no-holds-barred battle of lust and dirty games. In this twisted mind-fuck, trust is a luxury neither can afford.