Hey hello there guys I'm Warmachine375 and I present to you "Darkness and Sins" a crossover fanfic story between Nanatsu no Taizai and Overlord, both of my new favorite anime series I've watched so far and they're awesome as hell with their OPness! Oh my god, Nanatsu no Taizai has Season 2 announced that is coming this 2016 which I am so hyped of it and the Overlord anime is so enjoyable to watch lately, can't wait to see more episodes!

I think I might be the first one to make an Overlord crossover fanfic with Taizai! :D Hopefully there will more other fanfics with Overlord in the future to come around.

Summary: Taking a Job befitting for an Adamantite-ranked Adventurer which is to explore a faraway island continent of Britannia in the New World, Momon (Ainz Ooal Gown) and Nabe (Narberal Gamma) with Hamsuke finds themselves in a land being subjugated and oppressed by the Holy Knights and end up meeting with the Seven Deadly Sins trying to liberate the kingdom.

One-shot just in case.

Disclaimer: I own nothing of Nanatsu no Taizai or Overlord and their characters involved in the story unless I add OCs of my own. They respectively belong to Nakaba Suzuki and Kugane Maruyama the authors of the awesome manga and light novel series.

Enjoy and don't forget to review.

Chapter 1

Adventurer's Guild in E-Rental

Within the large guild hall where numerous Adventurers of every rank and type in the Re-Estize Kingdom gather around to eat and drink as much as they want, socialize with their friends and associates, rest and relaxation from work and take Jobs that benefited humanity, two prominent Adventurers entered the building while a large hamster-looking creature with a waited outside for its human masters.

A tall warrior wear a fully black body armor with purple and golden markings, and has a red cape on his back with two large swords and an elegant young woman with snow-white skinned, black-pony tailed hair wearing plain clothing and a brown cloak along with a katana sheathed at her side.

Both of them held Adamantite medals that displayed their high-ranking class that distinguishes them among all Adventurers of different respective ranks: Copper, Iron, Silver, Gold, Platinum, Mythril, and Orichalcum present in the guild.

They are the Darkness, an Adventurer group consisting of only two members of Adamantite rank though the team lacks a support type (divine) magic caster, they still managed to achieve several astonishing feats in succession, earning prestige among the Adventurers. They also registered the Virtuous King of the Forest and after it became the dark warrior's pet.

The armored man's name is Momon who is called the Dark Hero because of his black armor and great strength in battle believed to be that of the legendary Thirteen Heroes but in reality he is Momonga or better known as Ainz Ooal Gown, a very extremely powerful Elder Lich magic caster and the supreme leader of the Great Tomb of Nazarick as the Overlord after being transported to the New World with the Guild Headquarters and its NPC denizens after YGGDRASIL's server shutdown in its final moments of the game.

The young woman beside him is Nabe who is called the Beautiful Princess as people believed her beauty to be comparable to that of the Golden Princess of the Re-Estize Kingdom's royal family and is the strongest magic caster in the Darkness party as Momon's adventurer partner and also one of the strongest female Adventurers in the kingdom but in reality she is Narberal Gamma, a doppelgänger battle maid and member of the Pleiades, the battle maid squad of the Great Tomb of Nazarick.

And finally the large hamster-like creature is Hamsuke, the Virtuous King of the Forest that lived in the Tob Forest who is a part of Nazarick after becoming Momon's pet when Ainz subdued her way too easily with Despair Aura Level 1 Skill in their first encounter as he once believed that defeating the legendary monster might give him great prestige as an Adventurer but sadly he was disappointed of Hamsuke's appearance as a giant hamster although he saw some uses from her and others saw it as a great feat nonetheless.

Ainz Ooal Gown decided to become a famous Adventurer and lived in the city for a while, so that he can gathered more information about the New World and its' combatants, leaving Albedo in charge of Nazarick until he returns. He picked Narberal Gamma as his Adventurer partner. They disguised themselves as Adventurers under the names Momon and Nabe. They also decided to start their adventurer debut at E-Rantel and formed their own party titled Darkness there.

There, the Darkness have gained a lot of fame and reputation in the Re-Estize Kingdom, starting from the copper rank to adamantite rank in a fast rate when they confronted and killed the instigators Khajiit Dale Badantel and Clementine, thus foiling their plot to turn E-Rental into an undead city with a death ritual after their first job escorting Nfirea Bareare to Carne Village and to gather some herbs in Tob Forest with the Swords of Darkness who were later murdered and turned into zombies and one tortured to death by their hand; killed a powerful vampire, Honyopenokyo who was actually Shalltear Bloodfallen under an incomplete mind control of a World Class Item, A Downfall of a Castle and Country by Kaire, a member of the Black Scripture of the Slane Theocracy and freed her from its influence with a resurrection spell that costs 500 million gold from Nazarick's treasury after Ainz defeated her alone in a destructive battle; and fought off a demonic invasion of Jaldabaoth who was actually Demiurge playing along under Ainz' orders to stage an all-too convincing show of being the villain, on the Kingdom's capital of Re-Estize which further boosted their image as heroes.

They are considered to be the most powerful and strongest Adventurer party and the third adamantite-ranked Adventurer group in the Kingdom. With only a warrior and a magic caster, it is thought to be next to impossible to resolve the many dangerous incidents that they are capable of resolving that the other Adventurers believed them to be compared to the Thirteen Heroes and wouldn't be surprised if Momon is the adamantite of all Adamantites.

Scanning through the Quest Board filled with numerous Jobs available to specific ranks for Adventurers to take for several minutes, Momon took one notice of a certain parchment that got his attention and was curious to know about it since he has yet to understand the language of the New World.

Hmm... This one looks interesting. I wonder what it is... Might as well take it., the dark warrior thought as he then took it from the board and ask the details of the Quest that the Darkness is going to undertake to the woman handling the paperwork in her desk.

"Um... Excuse me miss. Can you please tell me the details of this Quest that my partner and I will take.", Ainz in his dark warrior guise asked while Nabe patiently waited for her master's orders and ignoring the glances from the male Adventurers admiring her beauty.

Scanning the paper's contents Momon had took from the Quest Board for a brief moment, the woman answered sweetly. "That would be the high-leveled Adamantite-ranked Quest Mr. Momon. It is to explore the famed and mysterious island of Britannia."

"Britannia?...", Momon questioned but in his thoughts. That's an old name for Britain or more specifically the United Kingdom from Western Europe. I didn't know there was such a name for a country like that in the New World.

"Britannia is an island continent stated to be located from the west in the coastal shore of the mainland and according to the travelers and merchants, it is a land where humans and demi-humans co-exist to a certain extent and is filled with extremely powerful warriors, knights and magic casters similar to the combatants on the mainland here, if not ridiculously strong compared to the Dragon Lords and the Thirteen Heroes notably.", she explained.

This intrigues Ainz Ooal Gown as he believed that the new land away from the continent might hold some of the answers he was looking for in this New World when he first arrived with the rest of Nazarick and decided to make an everlasting name for himself and the guild he represented altogether.

Perhaps there might be other Players from YGGDRASIL that might have brought out some Arthurian legend influences by them on the island continent and its inhabitants that gave the name Britannia or so he believed in his thoughts. If the mainland's human and demi-human nations have been greatly influenced by the Six Great Gods, the Eight Greed Kings and the Thirteen Heroes including the Boastful Sage of the Great Minotaur Nation when they arrived a long time ago before he came here, then it is a possibility.

Besides there were some other Players whose Avatars are modeled and customized to look similar or based off from the iconic characters from the legends of King Arthur and the Round Table in YGGDRASIL during the golden age of the popular DMMO-RPG (Dive Massively Multiplayer Online Role Playing Game) if he wasn't wrong.

"I see... Is it an isolated country?", Momon asked in wonder and curiosity.

"Yes, the nations in the mainland such as this kingdom, the Baharuth Empire, the Roble Holy Nation, the Slane Theocracy, the Dwarves Kingdom and the Dragonic Kingdom have heard of it and tried to make contact with Britannia but received no response and much of the land remains a mystery although there were trade from merchants who brought tales of it that brought their interest.", the woman replied.

"Hmm... Did the other Adventurers took the Quest similar to this?", he asked again if such Job was already taken before him and Nabe did.

The young desk-woman said with a sweet smile. "Yes, Mr. Momon. There were several Adventurer groups took the Job a decade ago but they came back dead or disheartened for some reason upon their return although they did brought glimpses of the country that might encourage future expeditions from the human nations. Perhaps you might be the first ones to fully explore Britannia."

Pondering on his thoughts for a few moments whether to take this Quest to explore the mysterious and isolated island continent of Britannia or not and then find a new one instead, Momon slammed his armored hand in his final declaration. "We'll take the Job."

Back in the Inn of Shining Gold where they stayed in their room with two beds each for them, Momon and Nabe dropped their Adventurer facades as Ainz Ooal Gown and Narberal Gamma after ensuring that no one eavesdrops on them to know of their true identities with many magical wards put in place.

"Is it wise to take the job Lord Ainz? This quest to explore Britannia held some ominous signs of danger ahead if the Adventurers came back dead or disoriented by some unknown great power lurking there and is very time consuming. We might be away from Nazarick for a long time.", the battle maid said in doubt and skepticism of her master's decision lately.

Removing his helm that revealed his skeletal face with a flick of his hand by magical means, Ainz reassured his partner, "Do not worry Narberal. In fact, I would like to see if there are some resemblances of Arthurian mythology in that island and if they have strong fighters like here. By first light, we'll set on a journey to Britannia after we settled reassurances from everyone in Nazarick. Perhaps there's a lot more about the New World than I thought."

Nabe nodded obediently to her master acting like he was thinking deeply in his thoughts and informed Albedo of Ainz's current activities and his decision to take the Quest of exploring Britannia via Telepathy firsthand so he will discuss with the rest of the Floor Guardians and Fluder Paradyne, a Prime Wizard and the greatest guardian of the Baharuth Empire who swore allegiance to the Overlord as his disciple to teach him all his magical secrets in exchange of offering everything he has and acted as his accomplice in aiding Ainz' plans of forging Nazarick as a new nation, about this once they return back to the Tomb.

Meanwhile Hamsuke sat in the stables to rest and wait for her masters' orders and call although there were some Adventurers and civilians gazing at the wondrous creature with awe and admiration of the Virtuous King of the Forest tamed by Momon the Dark Warrior and she was enjoying the attention.

And so, the Darkness readied themselves for the long journey ahead of them to come...

Author's Note: The first chapter of "Darkness and Sins" is done and the next update will coming soon if I believe this might be an interesting story. In this story's setting, Nanatsu no Taizai and Overlord universes are merged into one in the New World where Ainz Ooal Gown as Momon travels with Narberal Gamma as Nabe and Hamsuke and explores Britannia to learn more of the world he's transported to after YGGDRASIL's server shutdown of its ending as characters from both respective series are both overpowered in their own right.

I might need some help and assistance on estimating Overlord and Nanatsu no Taizai's Power Levels and the comparisons of their strengths and weaknesses in this story that I would most appreciate it. :D A merged world is better than a crossover to another world. It's much more easier to handle when writing fanfic stories. :D

Enjoy and don't forget to review. :D