Pokémon Day is February 27, marking the Japanese debut of Pokémon Red and Green.
The two Game Boy games launched in Japan on February 27, 1996, beginning the Pokémon video-game franchise. Outside Japan, the original pair was later released as Pokémon Red and Blue, while Japan also received Pokémon Blue and other updated versions.
The date is celebrated because the games—not the anime, trading card game, or a later international release—started the franchise. Pokémon Day therefore serves as the annual anniversary of the original Japanese launch. It is sometimes confused with the anniversary of the anime, whose first Japanese episode aired in April 1997.
The original games introduced the Kanto region, the first Pokédex, and the initial roster of 151 Pokémon. Their success led to sequels, animated series, films, cards, merchandise, and many spin-off games.