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.
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.
In Owari no Seraph fanfiction, Mika and Yuu's relationship is complex and deep. They have a strong bond that has been through many trials. Mika is often very protective of Yuu, and Yuu in turn cares a great deal about Mika. Their relationship can be seen as a mix of brotherly love and something more profound, which is often explored in different ways in fanfiction.
One popular theme is the exploration of their friendship in extreme situations. How they support each other when facing powerful enemies in the Owari no Seraph universe.
Love and friendship are also common themes. The female Yuu may form new friendships or fall in love in ways that are different from the male Yuu. These relationships can be a driving force in the story, either helping her grow as a character or presenting new challenges. Additionally, themes of survival in the harsh world of Owari no Seraph are present, with the female Yuu having to use her wits and strength to stay alive.
In fanfiction, Yuu's character might be developed by showing his vulnerability more when it comes to Shinoa. For example, he could be more open about his fears and insecurities around her. Shinoa, on the other hand, could be developed by showing her softer side towards Yuu. She might let down her tough - girl facade and be more affectionate.
One great Vampire Yuu fanfiction could be 'Yuu's Hidden Powers'. In this fic, Yuu discovers new and unexpected abilities that set him apart from other vampires. It delves deep into his character, exploring how he copes with these new powers while still maintaining his core values.
One great 'owari no seraph mika x yuu fanfic' is 'Fragments of a Bond'. It beautifully explores their relationship in a post - apocalyptic setting, delving deep into their unspoken emotions. The writing style is engaging and really draws you into their world.
One common theme is the exploration of their deep bond. Asuramaru and Yuu have a complex relationship in the original work, and fanfiction often delves into how they support and rely on each other. Another theme could be their adventures together in a post - apocalyptic world, fighting against common enemies. There are also some fanfictions that focus on the emotional growth of Yuu with Asuramaru's influence, like how Yuu becomes more understanding and empathetic.
You can try fanfiction websites like Archive of Our Own (AO3). There are usually a lot of works related to Yuu and Shinoa from Owari no Seraph there. Just search for their names on the site.