Character relationships are also a big trope. There could be friendships forming between characters from different universes. Maybe a character from Blue Exorcist becomes friends with a RWBY character and they learn from each other's cultures. Romance is also a common trope. It could be a love story between a character from Blue Exorcist and one from RWBY, which often involves them overcoming the differences in their worlds and abilities.
One popular trope is the crossover of characters' abilities. For example, a character from Blue Exorcist might use their exorcism powers in the RWBY world, or a RWBY character could learn about the demon - fighting techniques. Another is the team - up trope, where characters from both series join forces to face a common enemy. This could be a powerful demon in the RWBY universe or some sort of Grimm - like threat in the Blue Exorcist world.
The team - up trope is also quite common. Kratos joining forces with the RWBY team to take on a powerful foe. This allows for interesting battles and strategies as they combine their different fighting styles. Also, the 'lost in a new world' trope is popular. A character from either universe finding themselves alone in the other universe and having to figure out how to survive and get back home.
Another trope is the 'Soul Bond' trope. It's where the male reader character has some kind of deep, spiritual connection or bond with one of the Blue Exorcist characters. This bond can be the driving force behind many of the plot developments, like they are able to share powers or emotions through this bond.
For Highschool DxD, one of the most popular themes is the exploration of the different factions like devils, angels, and fallen angels. Fanfictions often create new storylines around their relationships and conflicts. In Blue Exorcist, the theme of family is big. Since Rin has a complex family situation, many fanfictions explore that further. Also in Highschool DxD, the theme of forbidden love between different species is quite common, like a devil falling in love with an angel.
One common trope is the fish - out - of - water scenario. The female Naruto, coming from a very different world, has to adjust to the rules and culture of RWBY. This often leads to humorous situations as she tries to understand things like Dust or the concept of Semblances. Another trope is the power - exchange. For instance, Naruto's chakra - based powers might interact in unexpected ways with the Aura and Semblance powers in RWBY.
You can start by looking on fanfiction websites like Archive of Our Own (AO3). It has a large collection of fanfics for both Blue Exorcist and RWBY. Just use the search function and type in the relevant keywords. Another option is FanFiction.net, which also has a good number of these crossover or related fanfictions.
A common trope is the 'mentorship' one. Harry, with his wealth of magical knowledge and combat experience, could mentor Ruby or other characters in RWBY. There's also the 'culture clash' trope. The different cultures of the Harry Potter universe and RWBY would lead to interesting interactions. For example, the way magic is perceived in each world and how they deal with threats. And the 'team - up against a greater evil' trope is likely, where they join forces to fight a powerful enemy that threatens both their worlds.
The 'fix - it' trope is quite popular. Since Summer Rose is a beloved character who had a tragic end in the original RWBY story, many fanfictions use time travel to let her fix things. For example, she could save characters who died prematurely.
Well, power - ups and leveling up are common themes. Just like in many games, the characters in Blue Exorcist gamer fanfiction often strive to get stronger in the game world. It adds an exciting element as they battle new and more powerful enemies. Also, exploration of unknown game areas is a theme. It allows for discovery of new items or secrets related to the Blue Exorcist lore.
One popular theme is the exploration of the characters' relationships. For example, the bond between Rin and Yukio can be delved into deeper in fanfiction. Another theme is the expansion of the exorcist world, like creating new types of demons or exorcist techniques. Also, the theme of self - discovery for the characters is quite common, as they grow and develop in the fan - created stories.
One common trope is the 'Fish out of Water' where the main character, often a self - insert or an original character, finds themselves in the RWBY universe and attracts the attention of multiple characters from the show, forming a harem. For example, a character from our world suddenly ends up at Beacon Academy and has to adapt while dealing with the romantic interests of Ruby, Weiss, Blake, and Yang.