For those of you that write fan-fictions?

Well basically I'm trying to find enjoyable things to help with expanding my imagination. I just want to write these for myself, not to show everyone... Does anyone have any ideas? like what you write about, and how you get inspiration for your ideas? Every time I attempt to write a fan fiction I end up making up a morbid, depressing story centering on my own made up characters instead of made characters... I just want to use made characters (anime) so I can write fun things that I enjoy. Thank you so much for the help ^^