There are several characters that could enhance the 'Shiro and the Black Lion fanfiction'. Kolivan, the leader of the Blade of Marmora, could be added. His experience and skills could be valuable in a mission related to the Black Lion. Narti could also be an interesting addition. Her ability to see through the eyes of others could provide a unique perspective in the story. And Romelle, with her knowledge of the Altean colony, might bring new information that is crucial for Shiro and the Black Lion's journey.
Well, a cool plot could involve Shiro and the Black Lion getting separated. Shiro then has to go on a quest to find the Black Lion while facing various challenges. Along the way, he meets new allies who help him in his search. And when he finally reunites with the Black Lion, they are stronger than ever and can defeat a powerful villain that has been causing trouble in their universe. It could also be interesting if there's a sub - plot about the history of the Black Lion that Shiro uncovers during his journey.
I'm not entirely sure if there is a specific fanfiction with 'Harry is a black lion animagus' but it's a very interesting concept. The Harry Potter fandom is vast and diverse. Some fanfictions are really well - hidden. You might have to dig deep into the archives of fanfiction websites or even contact some of the more dedicated Harry Potter fanfiction writers to see if they are aware of such a work.
There's a fanfiction where the black lion is actually the long - lost son of a former great king. He has been raised in exile by a group of friendly animals. When he returns to the Pride Lands, he has to prove his worth and claim his rightful place as the king. The plot thickens as there are other lions who want the throne for themselves and will stop at nothing to get rid of him.
There might be a fanfiction where the black lion is a mysterious traveler from a far - off land. He brings new ideas and ways of hunting to the Pride Lands. In this story, the black lion could face challenges from the traditional lions who are hesitant to accept change, but eventually wins them over with his skills and charisma. This type of fanfiction can explore themes of acceptance and innovation within the 'Lion King' universe.
One possible fanfiction could be where Harry discovers his ability to turn into a Black Lion Animagus during a dangerous encounter in the Forbidden Forest. He uses this form to protect his friends from a dark creature that has invaded the school grounds.
There might be a fanfiction where Keith and the Black Lion go on a special mission together that isn't shown in the original. They could face a unique enemy and have to rely on their bond to succeed. For example, they might encounter a powerful alien force that can disrupt their mental connection, and they have to find a way to overcome it.
Well, it's hard to say who the 'best' is as it depends on personal taste. But some popular authors might be those who have a deep understanding of the characters. They can capture Keith's complex personality and the mystery of the Black Lion really well.
Unfortunately, I can't recommend one directly. However, once you start your search, pay attention to the tags and summaries. If the summary seems interesting and the tags match what you're looking for, it's likely to be a good read.