Chief Master Sergeant John - 117 from Halo is often a popular character in these crossovers. His super - soldier abilities and leadership make him a natural fit in the chaotic and dangerous Warhammer 40k universe.
The Chaos Space Marines are also quite popular in these crossovers. Their dark and menacing nature contrasts well with the more 'heroic' characters from Halo. For example, Abaddon the Despoiler could be a major antagonist in a Halo x Warhammer 40k fanfiction, creating a lot of tension and conflict as he tries to spread the power of Chaos to the Halo universe.
In Halo Warhammer 40k crossover fanfiction, the Librarians from Warhammer 40k are quite popular. Their psychic powers can lead to some really cool interactions with Halo's technology and characters. They can sense things in the Warp, and how would that work when dealing with the more scientific Halo universe? Cortana from Halo is also a favorite. Her artificial intelligence is something that doesn't really exist in the same way in Warhammer 40k. So seeing her interact with the various tech - priests or even daemon - possessed entities could be really interesting. Additionally, Chaos Space Marines are often used for their menacing and unpredictable nature in crossovers.
Well, a cool storyline could involve the Flood from Halo and the Tyranids from Warhammer. Imagine if the Flood somehow made its way into the Warhammer universe. The different races in Warhammer would have to deal with this new, insidious threat that spreads like wildfire. And on the flip side, the psykers in Warhammer could potentially have some interesting interactions with the Halo universe's Covenant, who have their own sort of 'psionic' abilities with the Prophets and such.
In Warhammer 50k fanfiction, characters like the Sisters of Battle are quite popular. They are strong, devout warriors, and their stories of faith and combat can be really inspiring. There are also Inquisitors who are often central characters. They have the power to investigate and root out heresy, and their complex personalities, some being more noble and some being more morally ambiguous, make for great storytelling. Additionally, the Ork warbosses can be popular as they bring a lot of chaotic and violent energy to the stories.
Horus Lupercal is a very popular character. His fall from grace and the events leading up to it are often the focus of fanfictions. Another popular one is Magnus the Red. His connection to the warp and his attempts to warn the Emperor make for great story material. Also, Leman Russ is popular. His no - nonsense attitude and his relationship with his legion are often explored in fanfic.
The Spartans are also very popular in Halo Wars 2 fanfiction. Their super - human abilities and their role in protecting humanity give a lot of room for creative writing. Writers can explore their individual personalities, their training, and how they handle the various challenges in the Halo Wars 2 universe.
Ruby Rose is often quite popular. Her speed and scythe - wielding skills can be very interesting when translated into the Warhammer universe. Another popular one is Yang Xiao Long, with her powerful punches and her fearless attitude. In the Warhammer context, she could be a force to be reckoned with.
One popular character is Yvraine. She is often depicted in fanfiction as a powerful figure leading the Ynnari. Her unique abilities and her role in the Eldar's struggle for survival make her a fascinating character to write about.
In a Halo x Warhammer fanfiction, there could be a scenario where the Flood from Halo is unleashed in the Warhammer universe. This would be a huge disaster as the Flood has the ability to infect and assimilate almost any living being. The Imperium of Man in Warhammer would have to come up with new strategies to deal with this alien threat. Maybe they would try to use their psykers to combat the Flood's hive - mind. And the Halo UNSC forces might also get involved, bringing their own technology and tactics to the fight.
Master Chief is often a very popular character in Halo crossover fanfiction. His iconic status and combat skills make him a natural fit for crossovers. Writers like to put him in different scenarios and see how he reacts.
Cortana is another popular character. Her intelligence and her relationship with Master Chief are often explored in fanfiction. Some stories might focus on her evolution as an AI or her role in making crucial decisions during battles and strategic operations.