Unless you mean reducing the kai to dust
Good on ya for the dad joke. Need more of these around here.
Screed against electric vehicles aside (FWIW, "reduce" in that context is reducing CO2 equivalent/km...not km overall, but that's correct approach is a separate question), given what little we know about how the power system works, my best guess is that the system formerly known as MP Charge-kun is effectively all three Rs. Just gonna go on a little lore theorizing jaunt here:
Recycle: we know that magic generally leaves waste behind--expressly mentioned here, but a generic residual magic has been raised many times before. We had a mention of "low emission brooms" early on, too. Since we now know that residual magic is normally unusable waste, we see MPCK as a recycler able to convert some/all of that unusable residual back into usable magical energy. Not sure that's the same as the magi-nutrient that was brought up...some time ago.
Reuse: because this system is meant to work in tandem with a magical girl, her expended magic lost from inefficiency is put back to work, and consequently reused.
Reduce: Efficiency gains from the first two means overall need for magic energy is reduced. We haven't heard yet how usable magical energy is actually produced, but there doesn't seem to be any real concern about that part of the process. We do know that magical energy, like electricity and fuel, has a monetary cost with procuring it, reduced expenditures are generally a good thing for the financial side of the company.
Thanks for your patience with the long winded rant, there's something about this series that just gets me excited to talk shop