Region Free with circumvention utilities
Unlike the later add-on of the Turbografx-CD which was region-free, the Turbografx (aka PC Engine) itself was not, though this problem can be worked around with the aid of an adapter that simply goes into the slot, exchanging a couple of the pin-out settings around and letting Japanese HuCards work.
For American Turbografx systems (and the rarer PAL-designed Turbografx consoles that have PAL converters inside, released as location test systems but never on a wide scale – for all intents and purposes the two are the same region), it’s simply a matter of plugging the adapter into the console, and the card into that. For Japanese PC Engines, it’s a little more complicated – Japanese games don’t check what region the hardware is from (hence the ease of running them on US/EU systems), but American games do. There are several US-released games that don’t do this check, though they are few and far between. As such, a Japanese system has to be modified to play US games on top of needing an adaptor.