One possible fanfic could be about Mika and Krul forming an unexpected alliance. Maybe they have to work together to face a common enemy that threatens both of their existences. In this story, Mika might start to see Krul in a different light, not just as a vampire but as someone with her own motives and desires.
One common theme is survival. Given the post - apocalyptic setting of 'Owari no Seraph', many oc fanfictions focus on how the original characters endure and fight for their lives. Another theme is friendship. The oc often forms strong bonds with the existing characters, like Yuuichiro and Mikaela. For example, in some fanfictions, the oc and Yuuichiro help each other in battles and grow to trust each other deeply.
The Owari no Seraph Michaela novels often explore the theme of survival. In a post - apocalyptic world, the characters have to fight for their lives against various threats. There's also a strong theme of redemption. Some characters carry the burden of past mistakes and strive to make amends. Additionally, power and its consequences are explored. As the characters gain power, they also face the risk of being corrupted by it.
The ending of Owari no Seraph light novel is quite intense and leaves some room for interpretation. The main characters face significant challenges and their fates are resolved in a way that surprises many readers.
Overall, the Owari no Seraph anime follows the manga quite closely. Some characters' expressions and minor details might be a bit different, but the core story remains intact. The animation team did a decent job adapting it.
A crossover with 'Fullmetal Alchemist' would also be cool. Maybe the alchemical powers in that world could interact with the vampire and demon powers in 'owari no seraph'. The characters could be on a quest to find a way to either cure the vampires or use alchemy to stop the apocalypse that's happening in 'owari no seraph'.
You can try to find them in some local libraries. Some libraries have a collection of Japanese light novels. Another option is to look for e - book versions on legitimate e - book platforms such as Amazon Kindle or BookWalker. They often have a wide range of novels available for purchase and download.