One possible plotline could be Harry using his vegan lifestyle to promote animal rights in the wizarding world. He might start a club or campaign within Hogwarts to encourage others to be more conscious about their food choices.
Well, I'm not sure of specific 'harry is a vegan' fanfiction off the top of my head. But you could join some Harry Potter fan groups on social media. People there often share and discuss interesting fanfictions, and you might find some that focus on Harry being a vegan through their recommendations.
Vegan fiction is a genre of literature that often features themes related to veganism. It might include stories where the characters are vegans and face various challenges or adventures while adhering to their vegan lifestyle. For example, there could be a story about a vegan detective who uses their plant - based diet as a source of strength while solving crimes in a world that doesn't always understand or support veganism.
Comic books themselves aren't really something that can be classified as vegan or not. It's more about the materials used in their production and distribution.
I'm not entirely sure how much 'Johnny Test x Jillian Vegan' fanfiction exists. It really depends on how popular the idea is among the fanfiction writing community. Some writers might be drawn to the idea of putting these two characters together because of their different personalities and the potential for interesting storylines. But to find it, you'll need to be patient and search through various fanfiction platforms.