One common theme could be obsession. Since Billy is a yandere, there would likely be an extreme and often unhealthy obsession with Spencer.
I'm not sure of specific 'yandere billy x spencer fanfic' titles off - hand. However, you could also check out some fanfic communities on Reddit. Sometimes, fans share and discuss their favorite fics there, which might lead you to the 'yandere billy x spencer' ones you're looking for.
A common theme could be the exploration of their different personalities. Spencer Reid is often portrayed as highly intelligent and a bit socially awkward, while Eliot Spencer is more of a tough, action - oriented type. So, fanfics might focus on how they interact and learn from each other.
One good billy x spencer fanfic could be 'The Unlikely Bond'. It explores their friendship that gradually turns into something more special. The characters are well - developed, and the story has a great flow.
One great billy x spencer fanfic could be about their adventures in a fantasy world. They might go on a quest together, facing magical creatures and solving mysteries along the way.
A lot of Max x Billy fanfics also deal with the theme of protection. Billy might be seen as protective of Max in some fics, or vice versa. This could be in the context of the strange and dangerous events that happen in the show's universe. Additionally, friendship - turned - into - more is a popular theme. They start off as step - siblings who may not get along at first, but then their relationship evolves into something deeper and more romantic.
One common theme is friendship. Since they start off as sort of enemies in the original context, a lot of fanfics explore how they can become friends. Another theme is mutual understanding. They come from different backgrounds and have different personalities, so understanding each other is a big part of many stories. And of course, there's the theme of personal growth. Both characters often grow as individuals through their relationship in the fanfics.
One common theme is redemption. Billy was often portrayed as a troubled character in the original, and fanfics may explore his journey towards redemption through his relationship with Steve. For example, Steve might be the one to help Billy face his inner demons.
Some fanfics may have a theme of self - discovery. As they interact, both Billy and Rebecca might learn more about themselves, their strengths, weaknesses, and what they truly want in life, all within the context of their relationship.
You can try fanfiction websites like Archive of Our Own (AO3). It has a large collection of fanfics, and you're likely to find some great billy x spencer ones there.
First, think about the characters. Consider their personalities, likes, and dislikes. For billy and spencer, you might want to explore their unique traits. Then, come up with a plot. It could be a simple story about a day in their lives or a more complex adventure.