One possibility could be that Naruto inherits Alucard's incredible regenerative abilities. This would make him even more difficult to defeat in battle. He could also gain some of Alucard's vampiric powers, like enhanced strength and speed, which would give him an edge over his opponents in the Naruto universe.
The 'Naruto neglected Alucard' fanfiction could have a plot where Alucard is brought into the Naruto world by some mysterious force. However, the shinobi community is so focused on their own affairs like ninja wars, clan politics, and training that they simply overlook him. Alucard, feeling slighted, decides to use his vampiric powers and centuries - old knowledge to carve out his own place. He might first target the outcasts or those on the fringes of society, and as his influence grows, he starts to draw the attention of the more powerful Naruto characters, leading to a complex web of relationships and power struggles.
Perhaps the female Alucard is a threat to the Naruto world at first. She might be seen as an evil force because of her vampiric nature. But as the story progresses, she could learn about the values of the Naruto characters, like friendship and loyalty. And in turn, the Naruto characters could come to understand that she's not entirely bad and they could all work together against a greater evil that threatens both their worlds.
Well, it could be about Naruto having some of Alucard's powers. Maybe he has enhanced strength and speed like Alucard. And he could use these powers to protect Konoha in a new and unique way.
One possible plot could be that Naruto, during one of his travels, stumbles upon the world where Alucard exists. Alucard, being intrigued by Naruto's unique chakra, decides to test him. Naruto, on the other hand, sees Alucard as a powerful and somewhat mysterious figure. They could end up teaming up against a common enemy that threatens both their worlds, combining Naruto's ninja skills and Alucard's vampiric powers.
Friendship and cooperation are also common themes. Despite their differences, Naruto and Fem Alucard usually end up working together. They learn from each other and grow as characters. Their friendship might start out rocky but as they face challenges together, it becomes stronger. This theme is important as it shows that even those from very different backgrounds can become allies.
One common theme is power. Naruto has his ninja powers and Alucard has his vampiric powers. In the harem context, they often use these powers to protect the members of the harem. Another theme is loyalty. The members of the harem are usually loyal to Naruto and Alucard, and vice versa. Also, there's the theme of friendship. As they build the harem, Naruto and Alucard form new friendships with the characters in it.
Another possibility is that Alucard himself could become a sort of anti - hero/antagonist. Due to the neglect he faces, he could start to resent the Naruto world and its inhabitants. He might begin to act out, using his powers in ways that are harmful to the people. This would put him at odds with the main Naruto characters who would then have to find a way to either stop him or redeem him.
Well, you can try searching on popular fanfiction websites like FanFiction.net or Archive of Our Own. Just type in 'naruto female alucard' in their search bars and you'll likely find some relevant stories. They usually have a wide variety of fanfictions, so it's a good start.
Obviously Naruto, as the title implies he is the main focus. And since he is the son of Alucard, Alucard himself might be a major character, either in flashbacks or as a guiding force in Naruto's life.