Then maybe you could go with a background character style. I can only take example from anime but depending of the drawing style, you have characters with no eyes, no face, very simplistic doodle like face, or the character whole body being paint in a gray/black colourless monochrome. If you keep the gender ambiguous enough it could work ?
I don’t know how doable it can be depending of your idea.
So I asked some friends for help and so here more ideas :
- Having the main character turn their back from us with shoulder lenght-hair.
- Having something obstruct our field of vision like a ray of light or others characters, etc…
- Changing the perspective of the cover so it’s from the point of view of the main characters.
- Just having the shadow of the main character ; My friend asked that if you choose this one you should pay him 200 bitcoins
Btw, I don’t mind having a generic looking main character on the cover art.