Acceptance is also key. The fanfictions often deal with how the other ponies and creatures in Equestria accept their friendship. Some stories show initial resistance from others due to the differences between dragons and changelings, but eventually, through their positive example, acceptance spreads. It's a great way to explore themes of prejudice and overcoming it in a fictional world.
Friendship is a major theme. Since Spike and Thorax are from different species, their friendship shows how different beings can get along and support each other. For example, in many fanfictions, they help each other out of difficult situations.
Another theme is self - discovery. As they interact, both Spike and Thorax often learn more about themselves. In some stories, Spike might discover new aspects of his dragon nature through his relationship with Thorax, and Thorax might better understand his role as a changeling. This theme adds depth to their characters.
One common theme is friendship. Since MLP is big on friendship, fanfictions often explore how Thorax and Spike's relationship grows in terms of friendship. They might go on adventures together and learn about each other's cultures and ways of life.
There could be a fanfiction where Thorax and Spike form an unlikely friendship. Maybe Spike teaches Thorax about dragon traditions, and Thorax in turn shows Spike some of the secrets of changeling society. Their bond grows as they face challenges in a world that still has some prejudice against both of their kinds.
You can start by looking on popular fanfiction websites like Fimfiction.net. There are often a lot of My Little Pony - related fanfictions there, and you might be able to find some good Thorax x Spike ones.
One great Spike x Thorax fanfiction is 'A Unlikely Bond' which focuses on how they become friends in an unexpected way. It has a really heartwarming story that shows their growing relationship.
You can try searching on fanfiction websites like Fimfiction. There are often a lot of great stories there. Just use the search bar and type in 'MLP Thorax X Spike' and you should get a list of relevant fanfictions.
One common theme is friendship. Given their different natures, the stories often explore how they become friends. For example, in many fanfictions, Thorax's kind heart helps him break through Ember's tough exterior, leading to a great friendship.
One common theme is the exploration of their complex relationship. Given their history of rivalry and shared vampiric nature, many fanfictions dig deep into how they interact with and feel about each other.
Another theme is loyalty. Despite their differences and occasional rivalries, they are often shown to be loyal to each other in fanfictions. For example, in many stories, they will go to great lengths to protect one another.
The theme of acceptance is quite common. Spike has to accept the fact that he has a harem and the responsibilities that come with it. And the harem members have to accept each other as well. Another theme could be adventure. Spike and his harem often go on adventures together, facing new challenges and exploring new places. This adds an element of excitement to the fanfiction.
A theme that frequently shows up is the contrast between their species. Spike is a dragon and Rarity is a pony. This difference can lead to some really interesting cultural and physical differences being explored in the fanfiction. For example, how Spike's dragon nature might affect how he courts Rarity compared to how ponies typically do it. It also gives room for the exploration of acceptance, as they learn to accept each other's differences. Also, the theme of friendship is intertwined. Even if the relationship might be romantic in nature, their friendship is always at the core and is developed further through the story.