Well, 'Guilliman: Lord of Ultramar' is also a very good one. It gives a deep look into his character, his upbringing in Ultramar, his values that were instilled in him from a young age, and how those shape his actions and decisions throughout his life.
A common theme is leadership. Guilliman is a great leader, so many fanfics explore how he leads in different situations, like during battles or when dealing with political unrest in the Imperium.
One great piece of Roboute Guilliman fanfiction is 'The Primarch's Return' which delves into his post-resurrection experiences and how he readapts to the Imperium. It really captures his essence as a leader and strategist.
I don't have the exact answer off the top of my head. It could potentially be in one of the more recent series or standalone novels, but you'd have to check the detailed plot summaries or consult with other avid fans of the Black Library.
Here are some recommendations for Warhammer System novels:
1. Warhammer: Deciding to Take the Star Surround Subspace Route: This novel was loved by readers for its exquisite and beautiful text and fascinating plot.
2. [Warhammer: The Emperor's Unfilial Daughter]: This is a light novel, a derivative doujinshi novel that tells an interesting story.
3. Cypher: Lord of the Fallen Angels: This was one of the newest novels in the Warhammer 40K series.
4. Blazing Dawn: Tomb of the Martyrs, another new book in the Warhammer 40K series.
5. Lion: Son of the Forest: This novel is about the return of the Lion King.
6. " Proof of the Sun King ": This is a novel about the protagonist's transmigration to the Warhammer 40K world. He was chosen to be the 21st son of the Emperor, shouldering the mission of fighting against Chaos and searching for the ruins of the Ancient Sages.
7. " Crossing the Other World with the Warhammer System ": This novel tells the story of the protagonist Owen crossing into the Warhammer 40K world with the Warhammer 40K system in an attempt to change the world.
8. " Reborn in Warhammer 40K with the System ": This novel is a similar story. The protagonist is reborn into the world of Warhammer 40K through the system.
Please note that these recommendations are for reference only. The specific selection depends on personal preferences and reading preferences.
However, the Warhammer universe is vast and complex. Some novels might be a bit overwhelming for new readers at first due to the large number of factions, characters, and backstories. But overall, with a bit of patience, new readers can definitely enjoy the 'Warhammer Novels'.
4chan warhammer fanfiction contributes by giving fans a platform to express their creativity. They can expand on existing lore, create new characters, or even rewrite parts of the story they didn't like in the official version. It also helps to keep the fandom engaged and talking about different aspects of the Warhammer universe.