Well, often there might be a theme of discovery. Harry discovers his pyromaniac side and then has to figure out how it fits into his identity. Also, there could be themes related to power and control, as fire can be a very powerful and dangerous element.
One common theme could be Harry's struggle with his pyromaniac tendencies. Maybe he has to deal with the consequences of his actions, like accidentally causing harm with fire.
One common theme could be power. Fire is often associated with power in the Naruto universe, so in pyromaniac fanfiction, the characters might be obsessed with gaining more power through their fire - based abilities. Another theme could be control. Struggling to control the urge to use fire or the power of fire could be a big part of the story.
I'm not sure which specific 'harry is pyromaniac fanfic' to recommend. You could try searching on fanfiction platforms like Archive of Our Own. There might be various works with such a theme there.
The themes could include acceptance. The non - pyromaniac in the relationship has to accept the other's dangerous and abnormal behavior. Another theme could be self - destruction. The pyromaniac's love for fire may lead to self - destruction, and the story could be about how their love either saves them from this path or succumbs to it. There's also the theme of the forbidden, as pyromania is not socially acceptable, and their love is in a way forbidden because of it.
One common theme is the exploration of the relationship between Harry and the goblin society. It often involves Harry learning about the goblin culture, their laws, and their way of life which is very different from what he's used to in the wizarding world.
One common theme is the exploration of their different skills. Harry has his magic from the wizarding world and Natasha has her spy skills. Fanfics often show how they combine these skills to face challenges.
One common theme is acceptance. Many fanfics show how Harry's friends and the wizarding community gradually accept his Asperger's. Another theme is self - discovery, as Harry learns more about himself and his unique way of being in the world. And there's often a theme of friendship evolving to be more inclusive and understanding.
One common theme is the exploration of an unexpected relationship. Since they are from different backgrounds in the original series, fanfics often play with how they come together.
Friendship is a very common theme. Their relationship, which is a mix of mentorship and brotherly love, is often explored in great detail. For example, how Harry guides Eggsy and how Eggsy looks up to Harry.
One common theme is transformation. Harry often transforms into a bird or has some bird - like qualities. Another theme is freedom, as birds are often associated with freedom and Harry may experience a new kind of freedom with his bird - related abilities.
The theme of secrecy is quite prevalent as well. Given their positions in the wizarding world, any relationship or interaction between them would need to be kept secret. Fanfics play with this idea, creating tense situations where the discovery of their connection could have far - reaching consequences for both of them and the wizarding world at large.