I really like 'Alphonse's Redemption'. In this fanfic, Alphonse goes on a quest to make amends for things he feels guilty about. The author does an amazing job of expanding on his relationships with other characters in a believable way.
One characteristic is the expansion of their personalities. In fanfiction, we might see more of Edward's determination in different situations or Alphonse's kindness and wisdom. Another aspect is the world - building. Some fanfictions create new places and alchemy - related concepts around Edward and Alphonse. Also, the relationship between the two brothers is often deepened, showing their unwavering support for each other in various challenges and adventures.
The plot should also be engaging. It could be something like Alphonse facing a new threat or embarking on a personal journey of growth. For instance, a plot where he has to save a town using his alchemy skills in a new and unique way can be really interesting.
The dynamic between Edward and Alphonse in fanfics is quite interesting. They are brothers, but also partners in alchemy. Edward is the more active and often impulsive one, while Alphonse is more reserved. Fanfics may play with this dynamic, like having Alphonse be the voice of reason when Edward is about to rush into a dangerous situation.
Well, there's a fanfiction called 'The Bond of the Elric Brothers'. It focuses on the deep emotional bond between Edward and Alphonse. It shows how they support each other through various trials. Then there's 'Beyond the Gate', which imagines what happens after they pass through the Gate of Truth. It's really interesting as it gives a different perspective on their powers and destinies. There's also 'Edward and Alphonse: The Lost Years' that speculates on what they did during the time gaps in the original story.
A prevalent theme is the power dynamic between them. In some fanfictions, Edward is more dominant while Alphonse is more submissive, or vice versa. It adds an interesting aspect to their relationship. Also, the theme of redemption can be seen. They might be trying to redeem themselves through their relationship, especially considering the events in the original story that have caused them pain and guilt.
Love and relationships are also themes. He may depict different kinds of love, such as romantic love that is full of passion or family love that has a deep bond. His stories can also touch on the theme of social class differences, showing how people from different classes interact and the prejudices that exist between them.
One common theme is their unbreakable brotherly bond. It's often explored in different ways, like how they would do anything to protect each other. Another theme is their journey in alchemy. Since they are both deeply involved in alchemy, fanfictions often use this as a backdrop to develop their relationship further.