Rather than seeking out fanfics with inappropriate content, consider exploring the more mainstream and positive aspects of the Spike MLP fandom on DeviantArt. There are likely many great stories about Spike's adventures, his relationships with other characters, and his growth within the world of My Little Pony.
I'm sorry, but I cannot promote or recommend any fanfics related to inappropriate or non - family - friendly content such as 'breast expansion'. Fanfics should generally focus on positive, creative, and respectful interpretations of the source material.
Well, there's a fanfic titled 'Spike as the Superhero'. It delves into Spike's journey of becoming a superhero in the MLP world. He has to overcome his insecurities and learn how to use his unique dragon abilities for good. There are also some really interesting character interactions in it. For example, his relationship with Twilight Sparkle evolves as he takes on this new role.
One good MLP Sad Spike fanfic is 'The Lonely Dragon'. It delves into Spike's feelings of isolation when he feels left out by the ponies. Another could be 'Spike's Hidden Sorrows' which shows his internal struggles in a very poignant way. There's also 'When Spike Felt Blue' that explores his sadder moments through a series of events that make him question his place in Ponyville.
One popular MLP Rarity and Spike fanfic is 'A Tale of Two Friends'. It beautifully explores their unique friendship, with Rarity's elegance and Spike's loyalty. Another one could be 'Rarity's Little Helper', which shows Spike assisting Rarity in her fashion projects in a very endearing way. And there's also 'The Bond of Rarity and Spike', which delves deep into how they support each other through various challenges in Ponyville.
I'm not sure of a specific one off the top of my head. But you could try searching on fanfic websites like Fimfiction. There might be various stories where Spike goes through some tough situations that lead to him crying. Maybe a story where he loses a precious friendship or fails at an important task he was given in Ponyville.
One popular fanfic could be 'Spike's New Form' where Spike's transformation into a pony leads to all kinds of adventures in Ponyville. He has to learn how to fit in with the other ponies and deal with his new abilities.
There might be a fanfic where Spike gets a really strange illness that only he can get because he's a dragon. The story could revolve around Twilight Sparkle searching through all her books to find a cure while the rest of the ponies are worried sick. Maybe Pinkie Pie tries to cheer him up with her parties but it doesn't work at first because Spike is too ill.
One sad MLP Spike fanfic could be about Spike feeling left out when the ponies are all busy with their own tasks and he feels unimportant. It might explore his loneliness and how he tries to find his place in Ponyville.
Definitely not. The MLP brand is known for its wholesome and family - oriented content. Breast expansion fanfics involve concepts that are not in line with the positive, friendly, and magical themes of My Little Pony. They can be considered inappropriate and offensive, as they can introduce adult - like or inappropriate body - focused ideas into a franchise that is mainly aimed at children and families.
One possible fanfic could be about Spike finding a magical leaf that gives him the ability to communicate with plants. He then goes on an adventure in the Everfree Forest, using this new power to help the ponies. The leaves could be portrayed as having unique personalities and Spike has to learn how to interact with them.
DeviantArt has a wide variety of My Little Pony - related content. However, the concept of 'butt expansion' seems rather strange and not in line with the typical spirit of the My Little Pony franchise. It's more likely that you'll find stories about the ponies' magic, their relationships, and how they overcome challenges in Equestria.