I'm not really into that sort of fanfiction myself. However, some might find those that focus on Samus' adventures in uncharted planets interesting. They could include her facing new and strange enemies and using her skills in unique ways.
I'm not aware of any specifically. 'Lemon' fanfictions often contain inappropriate content which is not something I would recommend or promote. However, there are many well - written regular Metroid fanfictions that focus on Samus' heroics and her place in the galaxy.
A good way to develop their relationship is by showing how they grow together. Maybe Samus teaches Baby Metroid some things about the universe, like how to recognize different types of energy or how to avoid certain traps. And Baby Metroid could teach Samus about the Metroid way of life, such as how they sense their surroundings. This exchange of knowledge and experiences would create a deep and unique relationship between them.
Maybe Samus and Baby Metroid get separated. Samus then has to go through a series of dangerous challenges to find it again. Meanwhile, Baby Metroid is befriending some of the local creatures on the planet it landed on, and they help it survive until Samus arrives. This could show the bond between different species in the Metroid universe.
One interesting 'Metroid Dark Samus' fanfiction could be about her origin story in more detail. Maybe it explores how she was created and her first experiences in the Metroid universe. Another could be a story where Dark Samus teams up with an unlikely ally, like a small alien creature that helps her on a mission. And there could also be a fanfiction that focuses on her battles against Samus from a different perspective, showing her thoughts and strategies during the fight.
The best authors of 'Metroid Dark Samus' fanfictions are often those who can tell a great story overall. They have a good sense of pacing, so the story doesn't feel rushed or dragged out. They also know how to create engaging dialogue for Dark Samus and other characters. Some might be good at creating suspense and mystery, making readers eager to find out what happens next. Additionally, those who can make the reader feel something for Dark Samus, whether it's fear, pity, or admiration, are usually very talented authors.
Samus may develop by learning to see Ridley in a different light. In normal Metroid lore, Ridley is a pure villain, but in fanfiction, she could start to understand his motives or the reasons behind his actions, which could change her perception of him and thus develop her character.
I'm not really into this kind of fanfiction, but generally, in such a story, the focus might be on how Samus's character changes with the new relationship. Maybe it shows her more vulnerable side as she navigates the world of dating. It could also introduce some interesting new storylines related to her adventures and how her boyfriend fits into that world.
One popular theme could be the exploration of their complex relationship in a more dramatic or emotional way. Maybe Samus has to face her inner conflict regarding Ridley, who is usually her enemy, but in fanfiction, there could be a deeper understanding between them.
Honestly, I've never come across 'Samus Aran x Horse Lemon' fanfiction. Fanfiction usually revolves around more likely relationships, either within the same fictional universe or with some logical connection. This pairing seems so random that it's hard to imagine a large body of work around it. However, the world of fanfiction is vast and full of surprises, so a deep search on various fanfiction sites might be the only way to know for sure.