It's not a very common or mainstream fanfiction concept. 'Naruto' and 'Beast Boy' are from different fictional universes ('Naruto' from its own ninja - themed world and 'Beast Boy' from the Teen Titans universe). Combining them in such a way might be a very niche and creative idea that only a small number of fans might explore in fanfiction.
One possible plotline could be Naruto having some of Beast Boy's shape - shifting abilities in addition to his ninja skills. He could use this to his advantage in battles, for example, turning into animals to surprise his opponents. Another plotline might involve Naruto trying to understand his dual heritage and how it affects his place in both the ninja world and the world where Beast Boy comes from.
Well, Cyborg could also be a main character. He and Beast Boy are good friends, and Cyborg might have to adjust to his friend's new appearance and the changes that come with it. And then there's Robin. As the leader, he would need to deal with how Beast Boy's transformation affects the team dynamics. Maybe he has to figure out new strategies that take into account Beast Boy's new situation.
There are some fanfictions that might depict Beast Boy as a vampire beast in a post - apocalyptic world. He could be using his shape - shifting abilities in unique ways, like turning into nocturnal animals more easily since he has vampire traits. This type of fanfiction often delves into the darker side of his character and how he survives in a harsher world.
Maybe a girl with a similar power. For example, a girl who can communicate with animals telepathically. They would have a deep understanding of each other because of their shared connection to the animal world. They could go on adventures together, using their powers to help animals in trouble. Their relationship would be based on mutual respect for their powers and a shared passion for animals.
One possible fanfiction could involve Beast Boy and Storm meeting in a multiverse scenario. Maybe Beast Boy is on a mission in Storm's world and they initially clash due to their different powers and personalities. But as the story progresses, they start to understand and respect each other's abilities and end up working together to defeat a common enemy.
A common theme is the struggle between Beast Boy's humanity and his vampiric instincts. Since he's a beast at heart already, the addition of vampirism can create a complex internal conflict.
Maybe his dark secret could be related to his past trauma before he got his powers. For example, he might have witnessed something truly horrifying that made him the way he is.
Another reaction could be that he tries to hide his feelings by putting on a brave face. He might joke around even more to cover up the fact that he's really hurt. But deep down, his feelings are still damaged and this could lead to some bottled - up emotions that might explode later.
A fanfiction could also focus on their relationships outside of being superheroes. They could be having a normal day at the Tower, just hanging out. Starfire could be trying to cook something new from her home planet, Raven could be reading a book in the corner, and Beast Boy could be cracking jokes, which at first annoys Raven but then she starts to laugh.