Pokémon Red and Green Version

Pokémon Green (ポケットモンスター 緑 Pocket Monsters Green) along with Pokémon Red were the first Pokémon games to be released. Green was released only in Japan along with Red, and later when the games were translated for worldwide release was replaced with Pokémon Blue.

Plot
You are about to enter the world of Kanto where there are 151 Pokemon waiting for you. Your hometown is in Pallet Town. When you arrive a Professor Oak's lab, he will say that there are 3 Pokémon. They are Bulbasaur, Charmander, or Squirtle. Choose one of them in this game. Though your rival always picks the one better than yours. This happens in 3 starters games. You have to defeat the following Gym leaders:
 * Brock
 * Misty
 * Lt. Surge
 * Erika
 * Koga
 * Sabrina
 * Blaine
 * Giovanni.

Once you defeat all of the Gym Leaders, then you may proceed through Victory Road, then to the Pokémon League.

The Elite 4 are as follows:
 * Lorelei
 * Bruno
 * Agatha
 * Lance.

Once you defeated all of them, you will challenge your rival who is the Champion.

After you beat your rival, you become the champion of all, but you still can go beat the Elite 4 again.

Your last objective now is to complete the Pokemon Pokedex.

Version Exclusives
Pokemon Red                Pokemon Green

023 Ekans                    027 Sandshrew

024 Arbok                     028 Sandslash

043 Oddish                   037 Vulpix

044 Gloom                    038 Ninetales

045 Vileplume               052 Meowth

056 Mankey                  053 Persian

057 Primeape                069 Bellsprout

058 Growlithe                070 Weepinbell

059 Arcanine                 071 Victreebel

123 Scyther                  126 Magmar

125 Electabuzz             127 Pinsir

Trivia

 * Unlike Pokémon versions Red, Blue, and Yellow for the game boy, Pokémon Green's (or pocket monsters akai in Japan) storage media was never colored green like the others red, blue, and yellow respectively.
 * This is currently the only Pokémon game to be exclusively released in Japan.