There are fanfics that focus on the Xenos races. For example, a story about the Eldar trying to reclaim a lost artifact. It could explore their complex culture and psychic powers. Some fanfics also delve into the relationship between different factions, like how a group of Chaos cultists interact with a Rogue Trader.
One interesting Warhammer 40k fanfic could be about a Space Marine's journey of redemption. Maybe he made a mistake in a battle that cost many lives, and the fanfic follows his path to make amends. Another could be a story about an Imperial Guard regiment's fight against impossible odds, showing their tenacity and loyalty to the Imperium.
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.
Well, in Warhammer 40k mlp fanfic, the idea of the different pony races having to adapt to the harshness of the 40k universe is quite fascinating. Like the pegasi might use their flying abilities in new and unexpected ways in a battle - torn 40k setting. And the magic of the ponies could be a new and strange power in the eyes of the 40k characters.
One interesting story could be about the Space Marines' heroic battles against the Chaos forces. Their unwavering loyalty and superhuman combat skills make for great reading.
There might be a fanfiction where a group of Imperial Guardsmen encounter a Necron tomb world awakening. This story could explore the horror and confusion of the guardsmen as they face the ancient and powerful Necrons, and how they try to survive against overwhelming odds. It could also show the Necrons' view of the 'inferior' organic lifeforms.
There might be a fanfiction where a Primarch is reborn in a different era of the Warhammer 40k universe. In this story, they have to adapt to the new circumstances, which are very different from what they knew. They might find that the Imperium has changed in ways they can't fathom, and they have to fight new enemies and face new politics within the Imperium.
One interesting Warhammer 40k fan fiction is about a group of Space Marines who find themselves on a lost planet filled with ancient technology. They have to battle against not only the local xenos but also the temptation of the powerful and often dangerous technology. It's a great story as it shows the moral and physical challenges they face.
One interesting story could be about the rediscovery of an STC in a long - lost sector. It might involve a group of Tech - Priests on a quest to retrieve it and face various xenos threats along the way.
One interesting story could be about a Dark Eldar raid on a Imperial outpost. They swoop in with their fast ships, taking the Imperials by surprise. They capture slaves and valuable resources, leaving destruction in their wake.
Some fanfictions might center around the battles between different Primarchs. For instance, the confrontation between Horus and Sanguinius. In these stories, the authors often delve into the tactical aspects of their warfare as well as the emotional turmoil of the Primarchs. Additionally, there are fanfictions that show the Primarchs interacting with normal Space Marines in unique ways, perhaps mentoring them or learning from them in some cases.
The plotline about the Dark Angels Space Marine chapter is also captivating. They have a dark secret in their past related to the Fallen Angels. They are constantly on a quest to redeem themselves while still serving the Imperium. And the story of the Sisters of Battle, a female - only military order in the Imperium, is full of tales of faith, combat, and loyalty.