NPCs will enter Unconscious state when knocked out. For now, the only way to knock out an enemy is with the dart gun, but there will be other ways in the future. When an NPC is in this state, they will react to the proximity of a matching item when the player has it equipped. Now, that item is a placeholder dildo.
When the NPC detects that object, it "attaches" itself to it, allow for the player to move it around in 3D space, and the model will follow it while maintaining some constraints, like distance permitted to be moved, and have some attachment to the ground.
This way, sex can be interactive, on a 1:1 movement type ratio. Want it faster? Move the mouse faster. Want it from the side? Move yourself to the side. Want it faster, or slower? You can do that, only by moving the mouse.
This " spontaneous" sex moments are great for a game, where situations sometimes just emerge out of the randomness of all the things that are taking place. But it has one weakness, that it isn't as polished as a pre-made animation where the artist can control exactly how things move. One consequence of that here, is that you will get some clipping when the NPC goes through the floor, or is laying on an uneven surface.
To amend this weakness, I will also have some "pre-created" sex moments in game. Where things will be more controlled and will give different, more tailored experiences.