This is a relatively uncommon expansion pack. I don't know for sure, but I imagine this is geared more for the Tomy Pyuta mkII than the original, because the mkII lacks a true BASIC environment. But it will also plug into an original Pyuta just fine. To install this, it goes into the expansion port, not the cartridge slot (kind of obvious when you look at the connector). In addition to BASIC, it also provides printer connectivity.

In fact, it makes the original Pyuta behave like a Pyuta mkII in a couple of important ways. The opening animation screen and menu options are changed to match the Pyuta II. And it also uses English BASIC instead of the katakana-based BASIC that the original Pyuta uses.