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.
Well, one possibility could be that Shirou somehow gets transported to the world of The Lion King. He might initially be confused by the new environment full of talking animals. Maybe he tries to use his skills to help the lions in their fight against Scar. For example, he could use his swordsmanship to defend the pride from hyenas.
In a 'lion king meets humans' fanfiction, perhaps the lions and humans could form an unlikely alliance. For example, Simba might meet a group of kind - hearted humans who are lost in the Pride Lands. They could learn from each other, with the humans teaching the lions about new tools or concepts, and the lions teaching the humans about survival in the wild. It could also lead to a new understanding between the two species, resulting in a more harmonious co - existence.
In a 'Lion King 2 meets Humans' fanfiction, perhaps the humans are lost in the wild. The lions, led by Kiara and Kovu, find them. At first, the humans are scared, but then they notice that the lions seem to be showing signs of protection rather than aggression. The fanfiction could explore how the two species learn from each other. For example, the humans might teach the lions about some simple tools they use, and the lions could show the humans how to survive in the wild in terms of finding water sources and safe places to rest.
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.
It could be Scar. Since he is the main villain in The Lion King, in a fanfiction where Shirou enters this world, Scar would still be the one causing trouble for the pride. He might see Shirou as a threat to his plans of taking over the kingdom.
In a 'lion king meets humans' fanfiction, Mufasa could still be a crucial character even though he is dead in the original story. His spirit could guide Simba in dealing with the new situation of meeting humans. As for the humans, it could be a family who got stranded in the Pride Lands. Each member of the family has different reactions to the lions, and this family dynamic along with their interactions with the lions could form the main plot of the fanfiction.