You can try fanfic websites like Archive of Our Own (AO3). There are a large number of Castlevania fanfics there. Just search for 'Alucard Dracula Castlevania' and you'll get a list of relevant stories. Another option is Fanfiction.net, which also has a good collection of fan - created works.
The exploration of Alucard's heritage is a big theme. He is the son of Dracula, and fanfics often dig deeper into what that means for his identity. There's also the theme of the eternal struggle between light and darkness. Alucard, with his dual nature, is a perfect character to explore this. Some fanfics also focus on the history and lore of the Castlevania world, using Alucard and Dracula as central figures to unfold the secrets of the series' universe.
I really like 'Carmilla's Scheme in Dracula's Realm'. In this fanfic, Carmilla is depicted as a very cunning character who is constantly plotting within Dracula's castle. It gives a lot of depth to her character. As for Dracula, his power and brooding nature are well - presented. There's also 'Alliance of the Dark' which shows an unlikely alliance between them against a common enemy. It's a great read if you want to see them interact in a different way than in the original series.
A good fanfic in this context has to get the atmosphere right. Castlevania is a dark and gothic place, and the fanfic should convey that. When it comes to Carmilla and Dracula, their individual motives need to be clear. Carmilla might be seeking more power or territory, while Dracula could be focused on his grander plans for the vampire race. The fanfic could also introduce new elements to their story, like a mysterious artifact that changes their relationship. But it should all fit within the overall theme of Castlevania. The pacing should be appropriate too, not too slow that it bores the reader or too fast that important details are missed.
One great fanfic could be 'The Early Days of Alucard'. It delves deep into his childhood, exploring his relationships with his father Dracula and his mother Lisa. It shows how his upbringing in the shadow of Castlevania influenced his character development. Another interesting one might be 'Alucard's Childhood Memories', which focuses on his training and the first time he discovered his powers. It's a fascinating read for any Castlevania fan.
Some popular themes include the complex relationship between Alucard and Maria. Since Alucard is a half - vampire and Maria has her own powers, there's often a theme of power dynamics. Another theme can be the battle against the forces of darkness in the Castlevania world. They might team up to fight demons and vampires, which shows the theme of heroism and cooperation.
A good fanfic should include his relationship with his family. For example, how Dracula's actions and personality affected Alucard. Also, it should show his first encounters with the supernatural elements in Castlevania. His mother Lisa's influence on his values and his struggle to reconcile his human side with his vampire nature.
In fanfics, Alucard's character development often focuses on his struggle with his dual nature. He might start off as more withdrawn due to his vampire side, but as he spends time with Maria, he becomes more open. Maria, on the other hand, may develop her powers further. For example, she could learn new combat techniques from Alucard, which helps her become more confident in fighting the evils of Castlevania.