This is a compatible headphone unit for the WonderSwan, WonderSwan Color, and WonderSwan Crystal. A headphone unit is required to play music in stereo. The case is a 3D-printed compatible part. While perfect operation with all software is not guaranteed, it has been confirmed to work without issues with major titles such as Final Fantasy and Digimon. (Operation has been confirmed) The connection terminals on the main unit are prone to poor contact due to aging, so it's recommended to clean them initially for better recognition. If you previously requested a power supply unit or case set, or if you've purchased one before, please contact me for a discount.