A lot of younger fandom members don't know the slippery legal slopes like this. Many don't listen to the elder fandom members and just laugh that older people are in fandom. Please learn your fandom etiquette and the legality of fanfic/fanart which is an extremely gray area.
I am just now learning the original author/copyright holder of the media you want to write a fanfic for can actually sue you ??? I thought fanfics and fanarts are what builds a fandom which helps the og work get more popular, so Iโm gen asking why would they be against it ?