A more character - based story could involve Iron Man and an Imperial Tech - Priest. They could start off as rivals, each thinking their technology is superior. But then, when faced with a common enemy like a horde of Tyranids, they have to combine their knowledge. Iron Man's high - tech suits and the Tech - Priest's understanding of the arcane technology of Warhammer 40k could create some really cool gadgets and strategies to fight off the alien threat.
Another idea is a crossover where Thanos tries to get his hands on some of the powerful artifacts from Warhammer 40k. Maybe he wants the Emperor's sword or one of the powerful relics from the Adeptus Mechanicus. This would lead to a conflict not only between him and the Warhammer 40k forces but also potentially with the Guardians of the Galaxy who are also after these powerful items.
One interesting idea could be a story where the Space Marines from Warhammer 40k team up with the Avengers. Picture the Ultramarines and Captain America leading a combined force against a chaos incursion in New York. The Ultramarines' discipline and advanced weaponry combined with the Avengers' superpowers would make for an epic battle.
One idea could be a crossover with the Star Trek universe. The Tyranids could be seen as an extremely hostile alien force that the Federation has to deal with. Their bio - ships and swarming tactics would be a huge contrast to the more technological - based Starfleet.
One idea could be that the Infinity Stones are somehow connected to the Warp in the Warhammer universe. Maybe Thanos discovers a way to tap into the power of the Warp through the Stones, which brings the heroes of Marvel into conflict with the daemons and factions of Warhammer.
One idea could be a crossover with Star Wars. Imagine the Imperium of Man encountering the Galactic Empire. The two totalitarian regimes could have some intense ideological battles and epic space battles as well.
The gods in Warhammer 40k are on a whole different level of power. They can warp reality on a galactic scale. In Marvel, the Asgardian gods like Thor have great power, but it's not on the same scale as the Chaos Gods in Warhammer 40k. But if Thor were to face off against a daemon from Warhammer 40k, his lightning and strength might be enough to hold his own, especially if he had the help of some of his Marvel comrades and the technology and weaponry from Warhammer 40k.
Perhaps a Dark Eldar wych could form an unlikely alliance with a Space Marine. Maybe the wych has a personal vendetta against a chaos warband that is also targeting the Space Marine's chapter, and they decide to work together to take down the common enemy. This would involve a lot of tense moments as they try to trust each other despite their very different cultures and motives.
Perhaps an Imperial Inquisitor ends up in the Star Wars galaxy and tries to manipulate the Sith and Jedi for his own ends. He could see the Sith as a useful tool, not realizing how dangerous they truly are until it's almost too late. This could lead to a three - way battle between the Inquisitor, the Sith, and the Jedi.
One interesting concept is the crossover with other popular sci - fi universes. For example, a crossover with Star Wars could have the Imperium of Man facing off against the Galactic Empire. Another concept could be the combination of different Warhammer 40k factions in unexpected ways within the fanfiction. Maybe the Space Marines teaming up with the Orks against a greater threat.
One interesting plot twist could be the combination of the Force from Star Wars with the psychic powers in Warhammer 40k. Imagine a Jedi using his Force powers in the grim and dark universe of 40k, facing off against Chaos psykers. Another could be the appearance of Imperial Stormtroopers in a Warhammer 40k battle, their white armor standing out among the chaos. Maybe they could be mistaken for some sort of new xenos threat at first. And a third plot twist might be the discovery of a lost Star Wars planet in the Warhammer 40k galaxy, full of unique technology and species that both sides would be eager to control or destroy.
Thor and a Dwarf Lord would be really interesting. Thor with his god - like powers and his hammer Mjolnir could team up with a Dwarf Lord, who is known for his skill in forging and combat. They could exchange stories about their great battles and also work together to create some powerful weapon, perhaps using Asgardian and Dwarven forging techniques.
One interesting idea could be the combination of Naruto's ninja abilities with the high - tech and grimdark elements of Warhammer 40k. For example, Naruto's shadow clone jutsu might be used in a unique way on the battlefields of the 41st millennium. Maybe the clones could be used to infiltrate enemy lines or to overwhelm ork mobs.