This is a PC-Engine Wireless Joypad for use with the PC-Engine, or Turbo Grafx.
The controller uses 4 AA batteries and transmits signals to the included receiver which plugs into the joypad port.
The wireless joypad looks like a standard PC-Engine pad except it's thicker on the back side to accommodate the battery compartment and transmitter.
The wireless pad also shares the same functions as the original PC-Engine controller with a turbo function for the I and II buttons.
This required the reception unit PI-PD11 to operate.