Impact
Impact is being struck: a hand, a paddle, a belt, a cane, anything with weight or sting. The catalogue describes it as struck, and the rhythm and anticipation around it, and readers who tick it will tell you that the rhythm and the anticipation are most of what they came for. The walk to the chair, the instruction to count, the pause that goes on a beat too long, the difference between the fifth and the fifteenth. A list of hits is not an impact scene.
The theme runs from domestic discipline, with rules and consequences, through punishment inside a wider power exchange, to impact as pure sensation with no discipline frame at all. The engine does not assume which; the story and your setup decide.
How the engine handles it. With Impact ticked, the engine writes the scene with structure: rhythm, escalation, the count if there is one, the interior of both people while it happens, and the body's honest response, heat, breath, the point where it stops being bearable and the point past that. Implements are described precisely. Marks, if the story leaves them, are a fact the story state carries. Aftercare is written into the same scene, because the comedown is where an impact scene usually says what it meant. The spanking landing page is this theme as a genre. Your own limits, implements in or out, marks or no marks, never in anger, go in the special instructions and travel with the story.
Your stories are encrypted at rest. We can read them to write them. Nobody else can read them.