Imagine lying down on your stomach in bed and reading/watching TV/playing games, etc. while your favourite character is next to you, also occupied with something. Both of you are focused on doing what you’re doing, not really paying attention to each other.
At some point you feel them absentmindedly run their fingers up and down your back with very light touches that are barely noticeable and not very distracting. However, soon enough they start groping you, paying a big attention to your backside and attempting to touch you between your legs from behind. Eventually they shove their hand under your clothes and keep fondling you, stroking your anus with their finger teasingly but not doing much more, as though waiting for your reaction while you keep lying there and letting them do what they want.
After a while it seems it’s them who can’t take it anymore as they remove your clothes and start rimming you eagerly and then finger you hard.