One possible plotline could be Yuu struggling with his new vampire nature while still trying to protect his friends. He might have to deal with the thirst for blood and resist the urge to harm his comrades. Another could be that he uses his new vampire abilities to fight against the real enemies of the series in a more powerful way. For example, he could use enhanced speed and strength to take on the vampires that are causing chaos in the world of Owari no Seraph.
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.
His relationship with Mika would be very different. Since Mika is already a vampire, they might have a new understanding of each other. However, there could also be some jealousy or power struggle as Yuu adjusts to his new vampire status. With his human friends, like Shinoa and the others, they might be initially afraid of him. But Yuu would probably try his best to show them that he's still the same person who wants to protect them.
The 'Owari no Seraph' full story is quite complex. It begins with a world overrun by vampires. Yuuichiro is a feisty and headstrong character who has a deep - seated hatred for vampires due to the loss of his family. He enters the military academy to gain strength. Mikaela, his friend, is turned into a vampire against his will. As the story progresses, we see Yuuichiro facing numerous challenges, both physical and emotional. He has to deal with the power dynamics within the military, the devious plans of the vampires, and his own internal conflict about saving Mikaela. There are also elements of a larger conspiracy that slowly unfolds, which ties in with the history of the vampires and their relationship with humanity.
One aspect to consider in such a fanfic is the relationship dynamic. Crowley is a complex character in Owari no Seraph. When paired with a reader - insert, it can lead to interesting interactions. For example, his loyalty to his own kind might be challenged by his feelings for the reader. This could create internal conflict within him, making for a captivating story line.
One common theme is the clash of different power systems. In Naruto, there are ninjutsu and chakra, while in Owari no Seraph there are vampire powers and cursed gear. Fanfictions often explore how these powers interact when the two universes collide. Another theme is friendship across different worlds. Characters from Naruto and Owari no Seraph have to learn to trust and cooperate with each other.
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.