Toshiba HX-10S - branded plastic suitcase

Perhaps the clue is in the writing... The text on the cartridge appears to say 学習ソフトデモ用プ口グラ厶 which translates to "Learning software demonstration program" My guess is that it was a demo unit.

And in case your wondering what it says on the box itself, it says 東芝ホームコンピュータ which simply means Toshiba Home Computer.

ok thankyou, so I never saw that plastic box, and the mistery of the code remains.