Is this a PC Engine controller or what?

[wilykat]

Odd button layout, odd button names:
http://www.ebay.com/itm/PC-engine-controller-Accessories-JP-GAME-/311623063957?

And the pass through connector.  The last time I saw a game controller with a pass through mini DIN plug was for Macintosh ADB port. Looks like S-Video plug, and Macintosh ADB did have support for multiple devices on the same system so pass through connectors were the norm on some keyboard and game pads.

The picture doesn't show the plug itself so I can't tell if it's 4 pins, or PS/2 6 pins or something. I am pretty sure PC Engine does not have or supported pass through connector design.

[SignOfZeta]

It looks like a pad for PCs designed to operate via keyboard presses instead of an actual game/MIDI port, something that was occasionally indispensable but usually useless.

[Siskan]

Yes, it's designed to sit between the keyboard plug and the keyboard of a PC-98.