Such comics are usually of an adult nature, featuring sexual and pornographic elements. They are not within the realm of acceptable or legal content for widespread consumption or discussion.
One great Luna Lovegood story is when she believed in the existence of the Crumple - Horned Snorkack. It showed her unique and unwavering belief in the magical creatures that others might dismiss. Another is her time at the Battle of Hogwarts, where she fought bravely despite her rather dreamy nature.
There probably is. The world of fanfiction is vast and diverse. Writers might be intrigued by the idea of Luna Lovegood and Draco Malfoy being siblings. They could use this relationship to rewrite certain plotlines, for example, how their family dynamics would affect the events at Hogwarts. Maybe Luna's kindness could have an impact on Draco's actions, or vice versa.
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.