How to Unlock the Johto Region on Pokemon Emerald

With the introduction of new versions, new regions are also introduced. Kanto corresponds to Red, Blue and Yellow, and Johto corresponds to Gold, Silver and Crystal. Hoenn corresponds to Ruby, Sapphire and Emerald, and Sinnoh corresponds to Diamond, Pearl and Platinum. To collect every Pokemon available, you need to gain access to every region. However, it could be problematic because access to regions are local to their respective versions.

Defeat all eight gym leaders, and gain all eight gym badges as part of the main quest.

Defeat the Elite 4 to become and Pokemon champion of Hoenn.

Attain the National Pokedex after becoming the champion from Professor Birch at his lab. With the National Pokedex, you can see and record information about Pokemons from all regions or versions.

Fly to the Safari Zone (part of the Johto region); you will now have permission to enter and explore it. You will be able to see and to catch new Pokemons that you had not been able to before becoming the champion.