The Japanese version of Pokémon Blue (Japanese: ポケットモンスター 青) was the third Pokémon game released in Japan. It was only sold to the CoroCoro subscribers initially. It was released as a graphical upgrade from the original games, Pokémon Red and Green. Various other fixes were also implemented (glitches that were in the Red and Green). It provided the engine for the American Pokémon Red and Blue.
Most of the Pokémon sprites were redesigned.
The Catch rates were adjusted.
The Cerulean Cave was set up differently from the Pokémon Red and Green, using the layout that would be that of the English release of Red and Blue.