Another concept is the potential power they might have had. Given that the known primarchs were incredibly powerful, the lost primarchs could have had unique abilities that would have changed the course of the Warhammer 40k universe. For example, they might have had a different approach to dealing with the xenos threats, which could have led to a very different state of the galaxy.
Some fanfictions explore the idea of the lost primarchs having a secret legacy. This could be in the form of hidden technology or a hidden group of followers who still uphold their teachings in secret. It creates a whole new layer of story possibilities within the already vast Warhammer 40k universe.
Another popular interpretation is that the lost primarchs were secretly working against the Imperium all along. This could involve them allying with chaos or other enemies of the Imperium, and their disappearance was part of a long - term plan to undermine the Imperium from within. Fanfictions based on this idea often involve complex plots and political intrigue within the Warhammer 40k setting.
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.
Horus is often very popular in fanfiction. His fall from grace is a major event in the Warhammer 40k lore, and many fanfiction writers like to explore the reasons behind it more deeply. They might create alternate timelines where he doesn't fall or explore his relationships with other Primarchs in more detail.
Perhaps a key idea in this fanfic is the mystery surrounding the lost primarchs. Their very existence being a secret could be used to create a sense of intrigue. The fanfic might explore how rumors and half - truths about them spread among different factions, and how these rumors influenced the actions and beliefs of various characters.
One interesting concept is the exploration of alternate universes within the Warhammer setting. Writers can create different versions of the well - known factions and characters. For example, an Imperial Guard unit with unique weaponry or a Chaos Space Marine with a strange and unorthodox backstory. Another concept is the focus on the individual stories of the common soldiers or civilians in the Warhammer world, which often gets overshadowed by the grand battles and epic heroes.
Some interesting concepts in Warhammer 30k fanfiction include the loyalty and betrayal within the legions. There are stories that show how a single act of betrayal can have far - reaching consequences for an entire legion. The psykers in this setting also offer great potential for fanfiction. Their powers and how they are controlled or go out of control can be the focus of many stories. Additionally, the relationship between the Space Marines and the Mechanicum is another area that fanfiction often explores, with different takes on their cooperation and conflicts.
One interesting concept could be the evolution of the factions. For example, how the Space Marines might have developed new combat tactics or even new genetic enhancements. Another could be the exploration of new planets and the strange alien species that might be discovered. Also, the political intrigue within the Imperium could be a fascinating aspect, like the power struggles between different segments of the military or the Adeptus Terra.
One interesting concept could be the combination of RWBY's unique semblances with Warhammer's vast array of powers and races. For example, seeing a character from RWBY use their semblance in the context of a Warhammer battle. Another concept might be the exploration of how RWBY characters would adapt to the often darker and more brutal world of Warhammer.
One interesting concept is the idea of perpetuals themselves. They are immortal beings in the Warhammer 40k universe. In fanfiction, they can be explored in various ways, like their relationships with other factions. For example, how a perpetual might interact with the Imperium, either as an ally or a potential threat.
One interesting concept is the reimagining of characters' fates. For example, a fanfiction might explore what would happen if a certain hero who perished in the official End Times storyline was given a second chance. Another concept could be the exploration of different factions' reactions to the apocalyptic events. Some fanfictions might focus on how the Skaven, known for their self - serving nature, try to take advantage of the chaos in ways not shown in the official lore.