For "many many rotations", a pneumatic motor can act as both a compressor and motor. Spinning the motor causes air to be forced through a tube, one-way valve, and storage tank. Opening the valve allows the compressed air in the tank (potential energy) to flow back through the tube and motor, spinning it in reverse. As the number of rotations increases, the pressure increases, acting to stop the axle for a given torque. This presents a rotational limit, based on the volume of compressed gas, size of motor, size of tank, etc. For fast rotary motion this could work, but for slow motion, the pneumatic motor may "leak" and store little or no energy.
For "many many many rotations", a permanent magnet motor/generator -> DC rectifier -> battery (or supercapacitor) may work to store considerably more energy. Similar to the pneumatic concept, slow motion will not produce much charge. But the density of stored potential energy is much higher in batteries than it is air tanks.
There are significant losses in both of these, so there won't be enough energy stored to return the axle to it's original starting position.