Overlord x Log Horizon
While Shiroe and his whole guild was investigating a fairy ring, the thing activated and sent them to the New World. Ainz was walking down the main street of his capital just after he visited the newly hired dwarf rune smiths when a group of people suddenly appeared in front of him.
Overlord x Fate
For whatever reason, Ainz dies in the New World. A summoning ritual without a catalyst went wrong and grabs newly deceased Ainz's soul. How will the successor to the Ruler of Helheim and master of The Great Underground Tomb of Nazarick change the Holy Grail War?
Overlord x Fate
For some unknown reason, the overseer decreed that all of the summoning rituals must be done in Fuyuki. Coincidentally, a group of hardcore Overlord fans managed to discover the Holy Grail War. They believed that the participants are just people with extremely complicated case of chuunibyou though. By some freaky coincidence, all of the Grail War participants put their relic catalysts in ornate wooden boxes that had lid closed but not secure enough. Our weirdo Overlord fans group, being inspired by Luci Fer's work, decided to substitute copies of the Overlord light novels for the relics. Our poor participants didn't discover the little prank until after the summoning ritual because even during the ritual, the boxes where the relics were kept were sealed. For whatever forced coincidence, the summoning pushed through and was completed. Instead of getting regular Servants, all of the participants managed to summon one Overlord character. Due to the summoning that went haywire, the Avenger, Ruler and Shielder classes were also unlocked.
(Crossovers with this kind of theme are fundamentally built on forced circumstances. Making it believable is the key.)
Saber:
-Touch Me
-Warrior Takemikazuchi
-Cocytus
Archer:
-Peroronccino
-CZ 2128 Delta
-Aura Bella Fiora
-Entoma Vassilisa Zeta
Lancer:
-Bell River
-Shalltear Bloodfallen
Berserker:
-Herohero
-Albedo
-Sebas Tian
-Yuri Alpha
-Nigredo
-Lupusregina Beta
-Entoma Vassilisa Zeta
-Gargantua
-Cocytus
Rider:
-Beast King Mekongawa
-Momon (Momonga)
-Demiurge
Assassin:
-Nishikienrai
-Tabula Smaragdina
-Tigris Euphrates
-Solution Epsilon
-Aura Bella Fiora
Caster:
-Momonga
-Nuubou
-Yamaiko
-Tabula Smaragdina
-Punitto Moe
-Ulbert Alain Odle
-Mare Bello Fiore
-Narberal Gamma
-Lupusregina Beta
-Entoma Vassilisa Zeta
-Demiurge
Ruler:
-Punitto Moe
-Momonga
-Victim
-Demiurge
Shielder:
-Bukubukuchagama
-Albedo
-Sebas Tian
Avenger:
-Ulbert Alain Odle
Overlord x Attack on Titan
While Eren was detained and under the custody of the most excellent team in the whole of Survey Corps, Armin and Mikasa was restless and couldn't sleep. Seeing their condition, Conney suggested that they do something to occupy their mind. Armin went and re-read his prized book. Sasha saw him and they talked about the story he was currently reading. The girl was surprised when Armin told her that the book contained things that Armin's ancestors saw in their visions. Surprisingly, Armin came from a long line of sages that once gave advice to the royal family. At the very end of the book were instructions for a summoning ritual. Sasha suggested that they try to replicate the ritual but Armin shot down the suggestion and laughed at the idea. In reality, the idea was stuck at the back of his mind and later that night, he acted on it. He didn't expected that it would actually work. He looked curiously at the thing (Mr. OC/ Mr. Random Ainz Ooal Gown Member/ Momonga) standing on the writings he etched on the ground.
Overlord x Avatar: The Legend of Aang
In a completely different timeline, Avatar Aang's ties to the former Avatars was severed. Sensing this problem, Avatar Roku's dragon advised Aang to meditate and forcefully reconnect the broken bonds. By some (forced) miracle or another, he succeeded but a complication arose. The soul of Mr. OC, a high tier power gamer from YGGDRASSIL who had racial levels focused on ghosts, spirits and incorporeal races was taken by Aang accidentally. Now, Mr. OC is also inhabiting Aang's body just like the other Avatars though he can freely get out of the body since he was a stray soul originally. What will he do now?
Overlord x The Mortal Instruments
Valentine Morgenstern, through some sort of divine joke, used the Holy Grail instead of the Mortal Cup to create the Infernal Cup. He didn't knew though that the act of desecrating the blessed vessel would cause a wormhole to form. The Grail disintegrated, but in its wake, it summoned an otherworldly creature. From the creature's presence alone, which screamed death and despair, he could figure out that the thing was a high level demon. Valentine smiled thinking that his 'righteous' struggle against the Conclave would surely end soon and it would be in his favour. It was the last day of the servers. Mr. OC/Ulbert Alain Odle played one too many games before but none have made him happy the way YGGDRASIL did. In this game, instead of playing the part of cliche, hypocritical heroes, you could be a suave yet deadly villain instead. He looked at his claws and thought that he would certainly miss his razor sharp, platinum digits. He was about to log out when the clock struck twelve.
Overlord x The Mortal Instruments
Things have settled down quite a bit at the New York Institute after the last war. Jace, Simon and the others went back to Idris to tie up a few loose ends and Clary was starting to get bored out of her wits when an idea struck her. She was an artist through and through so she decided to step up her game. In a flash of inspiration, she decided to do street art instead of the usual sketching. Clary created some sort of mural and 3D painting on the pavement just outside the Institute. A part of her painting included a magic circle composed of a haphazard mix of circles, lines, runes and words. Clary thought that the design was harmless since it was aimless and the things on it were just random bits of stuff she saw on buildings in Idris, at Magnus' place and in her mind's eye. What she didn't knew was that her power of creating runes kicked in and the circle she created was a magic circle for summoning creatures from other universes. Their was a flash of light, a bit of smoke and bam! Someone from YGGDRASIL was summoned. Clary looked at Mr.OC/ Mr. Random Ainz Ooal Gown Member/ Momonga and wondered at what she had done. Luckily, the place was under glamours so no mundane could have seen what she did.
Overlord x Magi
It had been a few years and all dungeons were now conquered. The whole world was now preparing to dive into the bloody pools of warfare. The magi and their king candidates have been preparing for some time now. For now, everything was quiet but it was far from peaceful. The situation can be comparable to the calm before a storm. The tension was so thick you could probably slice through it. This was especially true for Sindria and its allies and the Kou Empire. Leam empire was weakened with the death of its aged and wise magi so it was just watching at the side lines. The two major powers of the world was continuing its struggle in key areas like Magnostadt while the Al-Thamen was spreading depravity all over the world. The tension heightened when Ali Baba discovered a new dungeon at the far end of Balbadd. Yunan, Aladdin and Titus met up and discussed the matter. They confirmed that none of them knew anything about that dungeon. Judal crashed in, calmly discussed with and listened to them. The three of them wondered what happened to Judal since he was so cooperative that day. The conversation quickly turned for the worse when Titus accidentally mentioned their king candidates. Judal showed his true attitude and the four of them even fought for a bit. Instead of being transported to the New World, The Great Underground Tomb of Nazarick was transported to Balbad. During the time before the shutdown, Momonga and Mr. Random Ainz Ooal Gown Member who has racial levels in Djinn racial classes were happily having a friendly match at the 6th Floor's Grand Arena and was distracted that they didn't notice the server shutdown.
Overlord x Avengers
For some reason, the Tesseract acting up didn't produce a black hole in the research facility it was in, not a destructive black hole at least. It still warped the local space-time but it produced a wormhole. When the Teseract's energy levels was stabilized, the Rosen-Einstein bridge it created pinched off at the center, created a black hole before the said hole evaporated as if it didn't existed in the first place. The event wasn't without complications as the said anomaly carried with it a peculiar creature (Momonga/Mr. OC/ Mr. Random Ainz Ooal Gown Member).
Overlord x Drifters
Suzuki Satoru nearly died of depression during the shutdown of YGGDRASIL. His body, now dead, was replaced by that of his in game avatar. Murasaki took a fancy on him and sent him to another world. Without his guild mates, guild base and pretty much everything, he found himself in another world while in the body of his avatar. Easy, being the smart ass that she was, sensed his disgust for his world and his intense longing. While he was sent as a Drifter, he is also tempted to join the side of Ends. Will he succumb to his depression and anti social disorder or will he lead the Drifters to victory?
Overlord x GATE anime
Instead of the Gate opening in modern day Japan, it appeared in Eryuentiu during the time of the Eight Kings of Greed instead. Now, will the eight legendary conquerors be able to add the lands beyond the Gate to their huge and growing empire? Will the lands beyond the Gate be able to satiate their avarice?
Overlord x Mass Effect
Commander Shepard was tasked with investigating a newly discovered Relay. Probes sent into it never gave any info and the Alliance, fearing the unknown, was desperate that they sent the Normandy on a suicide mission. It was just after the incident at Eden Prime happened The newly discovered Relay at the farthest edge of the galactic plane went nuts while the crew of Normandy was investigating it. Instead of shooting them across space to thr next Relay, it shot the ship outside of their own galaxy and into another galaxy 100 million million million light years away. Reports of a group of people who came out of a meteor was mentioned at a weekly report from Enri, the Chief of Carne Village. How will the arrival of the aliens affect the Ruler of Death's quest for world domination?