A recurring theme is the idea of self - discovery. When a character travels through time in the Grimm world, they often learn more about themselves. They might discover their true purpose, or face challenges that force them to reevaluate who they are. This is especially interesting when combined with the unique and often dark elements of the Grimm world.
Survival is also a big theme. When Naruto is thrown into the Grimm world, he has to use his skills to stay alive. This theme of fighting against the odds in an unfamiliar and often hostile environment is quite prominent. For example, in many fanfictions, Naruto has to face Grimm monsters much stronger than him at first. He has to quickly adapt and find ways to defeat them. Another theme could be the discovery of self. As Naruto navigates this new world, he learns more about his own abilities and limitations, and how he can grow beyond them. This is especially true when he encounters new magic or powers in the Grimm world that he has to incorporate into his fighting style.
One common theme is changing the past. Fans often write about characters trying to go back and fix things that went wrong in the original 'The 100' storyline. Another theme is the exploration of different time periods within the show's universe. This allows for new settings and character interactions.
One common theme is the struggle for acceptance. Since the OC is often different due to their Grimm - related aspects, they have to fight to be accepted by the RWBY characters. Another is power and its control. Dealing with Grimm - based powers can be a double - edged sword.
One common theme is adventure. Writers often send John Grimm and the OC on thrilling quests or dangerous missions. Another is romance. They might develop a romantic relationship between the two characters. And then there's the theme of friendship, showing how they bond and support each other through tough times.
Another theme is the power struggle. Faunus may have unique abilities related to their animal traits, and when combined with the threat of Grimm, there's often a struggle for power and control. Some fanfictions show Faunus trying to use their powers to protect themselves from Grimm while also fighting against human oppression.
The theme of destiny is quite common. Ash may travel through time to fulfill a certain destiny that he was unaware of in his normal timeline. He could be the key to preventing a great disaster in the Pokémon world's past or future. Additionally, the concept of cultural differences in different time periods is explored. He experiences different training styles, values, and ways of life as he travels through time.
One common theme is changing the past. In these stories, characters often go back in time to prevent a tragic event in the supernatural world from happening. For example, they might try to stop a powerful vampire from being created.
One common theme is the use of modern military knowledge in historical battles. For example, a character might use advanced weaponry concepts from the present in an ancient war.
One common theme is redemption. Firestar often goes back in time to correct past mistakes, either his own or those of the clan. For example, he might try to prevent a wrong decision that led to a battle or the loss of a cat.
One common theme is self - discovery. As Castiel travels through time, he often learns more about himself, his purpose, and his place in the grand scheme of things. For example, in many fics, he realizes things about his past actions that he didn't fully understand before.