One of the common themes could be transformation. The characters from 'Love Letter from Thief X' may have to transform their ways of thinking and acting in the 'Kenshi' world which is full of danger and different rules. Another theme could be power dynamics. In 'Kenshi', power is often a crucial factor, and when combined with the relationships from 'Love Letter from Thief X', it can create interesting scenarios about who has power, how it's used, and how it affects the relationships. Additionally, the theme of hope might also be present as the characters strive to make the best of their situation in this combined fanfiction world.
Common themes might include adventure. Characters from 'Love Letter from Thief X' are likely to embark on adventures in the 'Kenshi' universe. There could also be a theme of loyalty. As the characters face new challenges in the combined fanfiction world, their loyalty to each other or to new causes they discover in 'Kenshi' could be explored. And of course, there might be a theme of culture clash as the two very different universes collide.
I'm not sure about specific 'Love Letter from Thief X' and 'Kenshi' fanfiction. But you can try searching on fanfiction websites like Archive of Our Own. There might be some great works there that combine the elements of both.
One common theme could be forbidden love. Since the 'thief' aspect is involved, it might be that the relationship between the thief and the maid is something that society or their circumstances wouldn't normally allow. Another theme could be mystery. The presence of a love letter thief creates an air of mystery, like why is the thief stealing love letters and what connection does it have to the maid?
The 'love letter from thief x fanfiction' might be centered around the theme of redemption through love. The thief, who is typically associated with wrongdoings, could be on a path of change due to the love expressed in the letter. This fanfiction could explore different settings, from a gritty urban landscape to a more fantastical world, and how the love letter serves as a catalyst for change in the relationship between the characters.
I think it could be about a unique relationship. The 'thief x hiro' part might suggest a story where a thief has some sort of connection with Hiro. Maybe the love letter is a way for the thief to express feelings that are unexpected given their criminal nature. It could also explore themes of redemption or the power of love to change someone.
One plotline might be that the recipient of the love letter is a detective or someone who is supposed to be the thief's enemy. The love letter throws them off balance and they have to deal with their own feelings towards the thief. Or perhaps the thief is part of a group, and the love letter causes a rift within the group as they have different opinions on the thief's newfound emotions.
It could be about a thief who writes a love letter to Riki. Maybe it involves a story where the thief has some sort of connection or affection towards Riki and expresses it through this letter in the context of a fan - created story.
Often, there could be a mystery around the love letter thief. Maybe the maid discovers who the thief is in an unexpected way.
The unique relationship between the thief and Tatsuro is what makes it interesting. The idea of a thief having a connection with Tatsuro, perhaps a forbidden or unexpected one, can lead to a lot of drama and tension in the fanfiction.
One possible plotline is that the thief steals something important from Hiro at first, but then falls in love during the process. The love letter could be an apology and a confession at the same time. Another could be that they are childhood friends, but the thief turns to a life of crime. The letter is a way to come back to Hiro.
It could be about a thief who falls in love with Takuto and expresses his feelings through love letters. Maybe the thief has a change of heart because of Takuto's kindness or some special quality, and the fanfiction could revolve around their secret relationship and the challenges they face.