Which company published the Pokémon Trading Card Game in Japan when it debuted?

Media Factory published the Pokémon Trading Card Game in Japan when it debuted.

The Pokémon Trading Card Game first appeared in Japan in October 1996, with the initial Starter and Expansion Pack released on October 20. The game was developed by Creatures Inc. and was based on the Pokémon video-game franchise.

Media Factory was a Japanese publisher that handled the early domestic card releases. In the United States, Wizards of the Coast later published the English-language Pokémon TCG, beginning with the Base Set era in the late 1990s.

Nintendo is closely associated with Pokémon and helped manufacture or coordinate parts of the wider franchise, but it is not the answer to this specific publishing question. Creatures Inc. was involved in development, while Media Factory was the original Japanese publisher.