It's not ethical. The Warhammer 40k universe has a large and diverse fan base that includes a significant number of minors. Creating erotic novels based on it would not only violate the intended spirit of the franchise but also potentially expose inappropriate content to an inappropriate audience.
I'm not aware of any specifically 'wh40k erotic novel' series. The Warhammer 40,000 universe is mainly known for its science - fiction, action - packed and dark fantasy stories. Most official Warhammer 40k works focus on battles, lore, and character development within the grimdark setting rather than erotic content.
One popular 'wh40k fanfic' is 'The Emperor's Chosen'. It follows a group of Space Marines on a quest to retrieve a lost relic. Another is 'In the Shadows of Terra' which delves into the political intrigue in the heart of the Imperium. And 'Warriors of the Dark Gods' focuses on Chaos Space Marines and their dark deeds.
One common theme is empowerment. Since the Warhammer 40k universe is often male - dominated in the official lore, fanfiction about females often focuses on their strength and ability to make a difference. For example, a female character might rise through the ranks in the Imperial Guard against all odds.
Well, 'Ghazghkull Thraka: Prophet of the Waaagh!' is great. It focuses on the famous Ork warlord Ghazghkull. You get to see his rise to power, his strategic thinking (in an Orky way of course), and how he leads his Ork clans into battle, which is really exciting.
The clash of aesthetics. RWBY has a more anime - inspired, colorful look while Warhammer 40K is all about the gritty, dark, and gothic. When combined in fanfiction, it makes for a really interesting visual in the mind. For example, seeing Ruby's bright red cape in the middle of a Warhammer 40K battlefield full of dark - armored Space Marines.
First, study the lore of Warhammer 40k. Know the different factions like the Imperium, Chaos, Eldar etc. Then, come up with an interesting concept, like a new hero or a unique battle. After that, start writing your story, keeping in mind the dark and gritty tone of the 40k universe.
A great 'wh40k crossover fanfiction' is the one that combines it with 'Doctor Who'. The Doctor's time - traveling abilities open up all sorts of possibilities in the Warhammer 40k universe. He could potentially interfere with major events, or help in the fight against Chaos. There are also some crossovers with other fantasy universes like 'Dungeons & Dragons', where the magic systems and races from D&D are introduced into the 40k world, creating unique and often very chaotic storylines.
Talos is one of the main characters. He's a complex figure, often conflicted between his loyalty to the Night Lords and his own sense of morality. Another is Sevatar, a powerful and feared leader within the legion.
I'm not sure specifically as there isn't a common understanding of a 'wh40k wraithlord reading bettime story' without more context. It could potentially be about a Wraithlord in the Warhammer 40K universe engaged in some kind of bedtime - like activity, perhaps reading something related to their lore or a strategic document before 'resting' in their own mechanical way.