I'm the opposite. Every single one of my special interests has revolved around fiction, and more specifically, fictional characters. The characters I obsess over are either characters who I admire and want to emulate (like a role model), characters who I identify with, or some combination of both. I tend to think of my favorite characters as imaginary friends because I daydream about them so often and imagine them accompanying me when I go places. I also talk to them occasionally, though only when I lay down to sleep.
I can't imagine (no pun intended) a life without obsessing over fictional characters. I tried it last year, but all it did was make me miserable. I can't understand how people can obsess over things that have no personality, such as objects (even though it's common for other autistic people to obsess over objects), or areas of study (anything you can learn in school, such as math, science, writing, etc). I can sort of understand an obsession with animals, because I have owned pets my whole life (mostly cats) and have observed that all of them have what could be construed as "personalities". Plus there is the whole anthro/furry thing, so yeah, I can kind of comprehend that. But an obsession with objects or areas of study? I can't comprehend it.