Things You'll Need
Instructions
Load a copy of "Pokémon Ruby" into your Game Boy Advance and turn it on. While this is loading, insert a copy of "Pokémon Sapphire" into a second GBA and turn it on.
Connect both devices using a GBA Link Cable. These are available at most video game and electronics stores and online.
Walk into a Pokémon Center in both versions of the game and walk upstairs. Speak with the woman at the middle door to get to the Trade Center. When prompted, save your game on both GBAs and confirm that both players are ready to trade. Enter the door to the Trade Center.
Have the "Pokémon Sapphire" player walk up to one of the consoles and interact with it--repeat the process for the "Pokémon Ruby" player. Wait for the Pokémon screen to load. This screen shows which Pokémon both players have available for trade.
Use the D-Pad on the "Pokémon Sapphire" GBA to select Kyogre and press "A" to confirm. Select a Pokémon to trade for the Kyogre on the "Pokémon Ruby" GBA and press "A" to confirm. Follow the on-screen prompts to confirm that you really want to initiate the trade and watch the cutscene. When the scene is over, check your stock of Pokémon to see Kyogre.