These things slowly evolve I think. When I was 12 I remember breaking into the neighbors house while they were gone just to look at huge tits on their computer.
There has been many fetishes to come and go for me but a long lasting strong one for me has been sweat. I want to lick every last drop of sweat from a qt animes body. That slowly became I would gladly drink her pee and even blood.
Never got the scat though
From drinking her blood I have fantasies of slowly feeding off each other until there is a significant amount of my body made up of her and vise versa. You are what you eat right?
When we are sharing in all this we could even trade body parts, like swapping organs into each others bodies. Ultimately I would like to become one with her. Sharing an entire consciousness is the end goal for me.