One main feature could be its female - centric cast. Since it's about Toji, who are likely female characters, their stories and development would be a key aspect.
The 'light novel toji no miko' is an interesting piece of work. In such a light novel, there are often complex character relationships. The main characters, the Toji, may be part of an organization or a group. Their daily lives, including their study of certain arts or skills related to their role as Toji, could be depicted. There could be a hierarchical structure within the Toji community. And the story may be driven by the challenges they face, whether it's internal conflicts among themselves or external enemies trying to disrupt their world. It may also incorporate elements of Japanese mythology or traditional culture, which adds depth and uniqueness to the story.
Sure, Megumi discovers the truth about Toji being his dad in the manga. It's a crucial plot point that brings about various changes in Megumi's storyline and his relationships with others.
I'm not entirely sure specifically what 'dxd adult fanfic' is. 'DxD' might refer to a particular series (such as 'High School DxD'), and 'fanfic' stands for fan fiction. However, the 'adult' part implies it could be fan - created stories with mature or inappropriate content which is not suitable to discuss in detail.
The number of DxD novels can be a bit tricky to pin down. Different regions might have different releases and editions. Your best bet is to do a comprehensive search on popular book databases or consult with avid fans of the series.
The Highschool DxD manga has indeed finished. It wrapped up after completing all the planned story arcs and providing a satisfying conclusion for the readers.