One common theme is loyalty. Agni is extremely loyal to Soma in the original series, and this is often explored further in fanfiction. Another theme is friendship. Their unique bond is a central focus, like how they rely on each other. Growth is also a theme. As they face different situations in fanfiction, they might grow as characters, for example, Soma becoming more responsible with Agni's influence.
Sure. One popular 'Black Butler Agni x Soma' fanfiction is 'The Bond Beyond Duty' which explores their relationship in a more in - depth way, showing how their loyalty and friendship grow. Another one could be 'Agni's Promise' which focuses on the promises Agni makes to Soma and how they impact their journey together. There are also some on fanfiction.net that you can explore by using the search function for 'Agni x Soma' within the 'Black Butler' category.
One common theme is Soma's growth. Fanfictions often explore how he matures from a carefree prince into a more responsible and capable character. Another theme is his relationships, like his friendship with Ciel or his interactions with the other servants. And adventure is also a big theme, as Soma gets involved in various exciting escapades in the fanfictions.
Another theme is adventure. Since the Black Butler world is full of mystery and danger, many fics will have Snake and the reader going on adventures together. They could be exploring the dark alleys of London or trying to solve some mystery related to the Phantomhive household.
Common themes in such fanfiction are often centered around the unorthodox bond between Alois and Claude. There's the theme of the supernatural, given that Claude is a demon. This adds an element of the unknown to their relationship. Manipulation is another big theme. Both characters are prone to manipulating each other for their own ends. And there's also the theme of identity, as Alois' past and his current self, and Claude's true demonic identity all play into how they interact within the fanfiction.
One common theme is adventure. The male reader often goes on exciting adventures with the Black Butler characters. Another theme is friendship or bromance, as the male reader forms strong bonds with the likes of Sebastian or Ciel.
One common theme is mystery. The undertaker is a very mysterious character in 'Black Butler', so when paired with an OC, the fanfiction often delves deeper into the secrets of the 'Black Butler' world. Another theme is romance. Given the undertaker's allure, many fanfictions explore a romantic relationship between him and the OC. And also there's the theme of self - discovery. The OC might learn more about themselves through their interactions with the undertaker.
One common theme is loyalty. Finny's unwavering loyalty to Ciel is often a central aspect. Another theme could be protection. Finny protecting Ciel from various threats, be it other supernatural beings or human enemies. Also, growth is a theme. Ciel might grow as a person because of his interactions with Finny, learning about emotions like trust and kindness that he may not have fully understood before.
One common theme is the power dynamic. Alois is a complex character with a lot of power in the 'Black Butler' universe, and fanfictions often explore how that power affects his relationship with the reader - insert character. Another theme is redemption. Some stories might have Alois seeking redemption through his relationship with the reader.
One common theme is the reader character being involved in the dark and mysterious world of the Black Butler universe. For example, they might be a new servant in the Phantomhive household and have to deal with all the supernatural events there.
One common theme is mystery. Undertaker is a very mysterious character, and this often seeps into the fanfiction. The reader is usually drawn into his world of secrets. Another theme is the contrast between the darkness associated with Undertaker and the possible light or innocence of the reader - character.