Blastoise was used as the mascot of the Japanese Pokémon Blue version.
Japanese Pokémon Blue was released after Red and Green and featured updated in-game artwork and dialogue. Its development code, script, and artwork later became the basis for the international Pokémon Red and Blue releases.
This detail is easy to confuse with the international cover arrangement. International Pokémon Red featured Charizard, while international Pokémon Blue featured Blastoise. The Japanese release history is more complicated because Japan’s first pair was Red and Green, followed by Blue as a later special edition.
Blastoise is the final evolution of Squirtle and is numbered 0009 in the National Pokédex. Its water cannons and large shell made it a distinctive visual representative for the revised Japanese game.