Naruko in this fanfiction is most likely a character that the author has developed for the story. It might be inspired by other characters in the genre or it could be a completely new concept. Maybe she has certain unique abilities or traits that make her the target of being double teamed. For example, if it's in a fantasy setting, she could possess a powerful magic that others want to suppress by ganging up on her.
Naruko might also gain some vampire - like powers. For example, she could have increased speed and strength. However, she would also have to face the negative aspects. Vampires are often hunted or feared in many fanfictions. So she would have to constantly be on the lookout for those who would do her harm, and she would have to learn how to control her new vampire nature so as not to attract unwanted attention.
Well, it's hard to say for sure. The concept of 'porn-like' is quite subjective. Some might consider certain novels with excessive sexual descriptions as such, but it depends on individual perspectives and cultural standards.
In many places, 18+ porn comics are considered illegal. This is because they can have a negative impact on society and violate moral and legal standards.
There's also the possibility of pairing Naruko with Sirzechs. His powerful and noble nature could contrast well with Naruko's more brash and energetic personality. It could lead to a story where they have to work together to solve a major problem in the DxD world, and in the process, develop a deep connection.