I give myself unnecessary anxiety?

Are you saying that trying to come up with the fanfic is giving you more anxiety? As someone who's suffered from bad anxiety since I was 16 years old, I find creative projects really helpful, but I'll read a familiar book, or watch a familiar show before going to sleep, to get to a safe place in my head. Working on creative projects is calming throughout the day though, because I get to connect with myself through them.

I think you're putting too much pressure on yourself. Watch some of your favorite mortal Kombat gameplays or read some of the lore again. It'll come to you when you least expect it.