A torsional coupler can be dimensioned for securement between a rotational motion source and a rotational motion target. The torsional coupler can include a first end component and a second end component that can cooperatively interengage one another such that such that rotational motion imparted on the first end component is transmitted to the second end component. Interposed between the first end component and the second end component is one or more force-transfer elements through which torque and/or other rotational output is transmitted. The one or more force-transfer elements can include one or more pressurizable elements into and out of which pressurized fluid (e.g., gas and/or liquid) can be transferred. Additionally, or in the alternative, the one or more force-transfer elements can include one or more biasing elements having a positive stiffness and one or more biasing elements having a negative stiffness. A rotary power transmission is also included.