@jinminmoon I'm not an expert nor do I know anything about dnf at all. But changing it from an original work to a fanfiction, will change the target audience. On one hand, you'd be appealing to the general public with different interests and standards in what they read. On the other, you'd be appealing to a group of people that you're familiar with. Sure that they too, have different interests and standards in what they read but at least being in the same fandom will let you know what they like and will be able to relate to them more.
Of course, the target audience is just a small part of it. A huge part of the story depends on how you write and since you've been working on it for a year, I believe it'd be really nice!! Best of luck