I always avoid fanfics like plagues because most, if not all are just hot garbage that skews so far off-course of the original work that for sometime, I actually wanted to write an email asking the author to just create an original work instead.
I understand it is hard to think of your own characters, hell I have been churning new characters in my never-gonna-published work that is just someone you knew in other works, only with a diff paintjob and some tweaks that might or might not totally break the character in half. It is alot easier to just say "hey, you know this bunch of guys, now I am going to insert myself (please don't lie) into the group".
I do this a lot in my own imaginations (be it Y/N and SI) as a child and up until now, it took me a brief moment to think about the plot and how much it sucks, which is why it is always locked inside of my head like my mentally unstable relative underneath the house's basement.