My fantasies seem to span a range.
But mostly I believe they relate to - Couples + One or more.
Mostly because of the intricate interactions and many possible combinations . MF-mf, M-ff Mm-f etc
Willing , unwilling observer or participant.
My first art/story post here is one that’s encompasses them well.
The range of emotional dynamics if they are married, strangers or friends. Maybe the psychological aspect of it .
Inviting someone in to spice things up, big or small.
Being found or used etc. Helpless or in control.
Seeing a partner enjoy themself with a tiny or two, or being enjoyed by one ( or a couple ) or more than one full size one, is erotic to me.
Not this its exclusive to this “couples thing”, but I feel there is a discovery of ones secret desires of being small, or having small ones at your service. Becoming uninhibited , surprised by the other persons naughty unspoken desires.