One common theme is friendship. Since they are both characters in the RWBY world, many fanfictions explore how they become friends and support each other. For example, Penny might help Ciel with her training, or Ciel might stand up for Penny when others misunderstand her.
Well, Archive of Our Own (AO3) is also a great place to look for rwby penny x ciel fanfiction. It has a large collection. You can filter the results by tags such as 'Penny', 'Ciel' and 'RWBY' to narrow down your search and find the stories that really interest you. Some stories might involve them going on adventures together or having deep conversations that strengthen their bond.
One common theme is friendship. Ruby and Penny have a unique bond in the RWBY series, and fanfics often explore how that friendship develops further. Another theme is adventure. They might go on quests together, fighting Grimm side by side.
One common theme is friendship. Despite their differences, many fanfictions explore how Mercury and Penny could form an unlikely friendship. Another theme is redemption. For Mercury, who has a rather complex and often villainous role, fanfictions may show him on a path of redemption with Penny's influence.
Redemption is also a theme that appears sometimes. Undertaker may be portrayed as having a chance at redemption through his interactions with ciel. This could involve him trying to make up for past wrongs or helping ciel in a way that goes against his previous actions. Fanfictions might explore how this redemption arc could play out and how it affects both characters.
One common theme could be identity. Since there are two Ciels, the question of who is the 'true' Ciel might be explored. Another theme could be family, as they are brothers and their family history and relationships play a role.
One common theme is the exploration of Penny's unique existence. Since the SI is reincarnated as Penny, there's often a focus on her robotic nature and how it affects her perception of the world. Another theme can be friendship, as Penny was always eager to make friends in RWBY. The SI might have a different take on forging relationships within the RWBY universe. Also, there could be themes related to identity. The SI has to come to terms with being Penny, who has a pre - established identity in the show.
In some ciel x lizzy fanfictions, there is a theme of self - discovery. As they interact more, they learn more about themselves. Ciel might discover a softer side of himself because of Lizzy, and Lizzy might find more strength in herself. Also, the theme of loyalty often comes up, as they prove their loyalty to each other in different situations in the stories.
Love and devotion are very common themes. Most fanfictions focus on how deeply Elizabeth loves Ciel and vice versa, despite all the difficulties they face.
One common theme is the idea of the OC being a source of change for Ciel. Since Ciel has a rather dark and set - in - his - ways personality, the OC often comes in and shakes things up, like bringing more light into his life.
One common theme is the idea of opposites attracting. Sheldon is very logical and Penny is more emotional and social, so many fanfictions play on how these differences can draw them together. For example, in some stories, Penny helps Sheldon understand emotions better, while Sheldon helps Penny with intellectual things.