Disclaimer: This is just a fanfiction of an cross over between Overlord (the anime and light novel) and the Warhammer 40k verses. I will take any feed back in the review section.

Sorry for the delay the research for necron vs slanessh take me to a tau rabbit hole

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Over sixty millennia have passed since Cocytus's last battle, a most brilliant one that was, to fight along with the supreme being and most of all along with his father the great warrior. The battle to shatter the C'tan god to thousands of shard is deeply engraved in his mind as one of the most treasured memory.

Cocytus the leader of the lychguard unit, consists of eight hundred thousands warrior, this number may be considerably lower when the court inevitably split to reclaim it lost world. And when that time come Cocytus wish to nominate some of his more trusted retainer to ventures out seeking for his father and the other supreme being. Although he wanted to personally embark on such a mission, the protection of the last remaining supreme one and his dynasty take priority over any ambition he might have.

'Demiurge might have already organize such a force.'

Their no doubt that his fellow general and guardian Demiurge, one of the most genius mind of the dynasty have already prepare for such a task. Cocytus belive that Demiurge will accomplish his task with aplomb, and their is no doubt about his loyalty.

"I. Have. Arrived."

Cocytus announced in front of the gate leading to Demiurge commanding chamber, the door open and he walk further inside.

The chamber is barren with only a large throne in the middle, standing beside it is the figure of Demiurge, he stand straight with arm warped around behind himself. Demiurge turn his head and give a brief nod to welcome Cocytus, Numerous light source flashes countless time from under his formal suit, and in response Cocytus also do the same from his bare chest, through this unique way of communicating the entire battle strategy and some banter is conveyed in just a few second.

"Why. Don't. We. Just. Communicate. This. Way?"

"I believe that this would be a much slower way of communication for this trying time. Lord Momonga suggests that we should use this way to express ourselves, but could you agree that it brings problems along with it."

"Watch. Your. Voice. Unit. Demiurge. You. Are. Treading. A. Fine. Line."

"My apologies, I believe that the Shaltear problem clouded my judgment, and I believe that lord Momonga have his own reason to encourage us to communicate this way. But in the duration of this operation, I would like to use the binary communication method, for time saving reasons."

It is true that his reason is to save time, but the deeper meaning for Demiurge is just wants to have a proper conversation with Cocytus without the pause in between his words. He knew that such a gimmick was created by the supreme being who granted them these bodies and by making alterations to it is like saying the supreme being's work is flawed, and that is an insult to them.

"Hmm. That. Is. Fine."

Cocytus agrees confirming his friend's loyalty toward their master and starts blinking light again to plan for the finer details of this operation. Their conversation lasted for only a few seconds more, then Cocytus promptly leave to arrange his lychguard unit and their master ground troop.

Cocytus wanted nothing more than to mobilize the entirety of the lychguard legion to stomp down these beings, but sadly only a small amount of his warriors had awakened. This upcoming battle is very winnable yet with his current small yet elite lychguard warriors, they might suffer a substantial loss. Because of the lack of close combat units and this battle have to be finished as fast as possible, the lychguards will have to be the vanguard, and judging by the look of their enemy, it seems like their evolution is whole hearty developed for close combat. Against such an unknown, being evolved for combat, seething with the chaotic power of the inmaterium, and not to mention the size of their force nearly double their own, if not for the supreme being carefully awakening their force, Cocytus might have to fight with an even smaller and weaker army.

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To think of the day when little Londes would call upon the dark prince, to experience such joyest occasions this keeper of secrets waste no time gathering whatever force it can muster and rip a sizeable tear in reality, because for hundreds of year, it have lusted for this single space marine. They have fought on many occasions, not wanting to damage such bounty the keeper have held back quite a bit, for a single love tab without moderation will inevitably maned it loved, it has been many time banished by the hand of Londes, his adorable expression of triumph make the whole efforts to reassemble it physical bodies all the more worthwhile.

It mere present corrupt the large area it standing on but with a bit of effort it power of corruption spreads to the entire world. The wave of ecstasy, pain and carnal desire washed over the planet surface, embolden the follower of the dark prince to much more intense debauchery. not sparring the regular citizenry, their deep dark desire manifest in to action, leading to rape, murder and torture, all being inflicted onto the nearest target no matter the gender, blood relation nor species.

Feeling its daemonic essence reaching the far edge of the continent, the keeper of secret let out a sensual moan as the world around it filled with debauchery and violence.

"How has this world evaded the gaze of the dark prince for so long, to never felt the ecstatic touch of him for its entire existence, truly it is a maiden world. And for me to be the first to defile her... he he he. she will be well taken care of, so much so that no one else other from me could ever satisfy her."

In the middle of the ruined city, the keeper stood there satisfied, pleasuring itself to the harmony of pain and pleasure released by the human population.

With a sudden sound of air splitting, a flying vessel is approaching at unimaginable speed. If the keeper were any other inferior being it would not sense any microscopic change especially one so faint and so far away. Issuing a mental command to its legion consisting of three hundred thousand deamonette and lesser daemon of slannesh, ordering them to put away their toy and be ready for another round of massacres. Its order is met with a loud cheer followed by an even louder scream of agony as the slanneshy daemon celebrates by forcing their victim to experience even greater pain. No matter what these human shoots at them it would be meaningless, some lesser daemons might have their physical form destroyed and their essence return to the immaterium, if it is not a head-on clash of glorious melee combat where the will of each individual overlaps and overpower each other, then they will eventually emerge victorious.

The keeper stood there awaiting the first move of the human but instead met with a green light crackling with bolt of electric splinter, the wave of energy missed the keeper by a block of housing but still disintegrated more than half of its body. Falling to its knee the keeper stops focusing on the spreading of the corruption and is solely devoted to reconstructing its mangled body.

Due to its experience the keeper quickly reconstruct its body, and immediately stood up witnessing the sheer destruction caused by a single attack. The energy wave disintegrates a large chunk of the city and thousands of daemon, after banishing a part of the keeper assault force, its enemy emerges from the outskirts of the city.

Rows by rows of necron rally in perfect unison gause weapon arm and ready, they enter the city uninterrupted. Some humans who are lucky enough to survive the initial strike and still strong enough to crawl themselves out of the collapsed building find themself being crushed and trampled to death at the foot of the incoming legion of metal skeletons. Any daemon still hadn't been banished jumped at the incoming legion, their quickly close the distance and slashed against the necron with their razor sharp claw blade, managing to damage some of the incoming metal skeletons but the daemon is immediately cut down by the axe head attached the front of the necron rifle.

Knowing that their charming ability is next to useless against this emotionless enemy, the keeper orders it army to take cover and be ready to charge head on against this robot legion.

Feeling the slight changing of air pressure, the keeper immediately twisted its body, bearly avoid the blade aiming for its head. The green hue of the blade reveal its foe to be a necron, continuing the momentum of twisting its body the keeper use its claw to cut off the leg of the assassin. But its lightning speed attack missed its target, the necron simply stepped back before the swing even started, this simple action alert the keeper of the danger level of this soulless being. As it army is being besieged at all front the keeper bring it focus solely on to the warrior of it, abandoning the command of its forces and believing in the might of number it have, the keeper draw it witstealer sword ready to attack.