Johto was introduced in Pokémon's second generation of main-series games.
The region debuted in Pokémon Gold and Silver for the Game Boy Color, released in Japan in 1999 and internationally from 2000 onward. Pokémon Crystal, an enhanced version, followed in Japan in 2000 and elsewhere in 2001.
Johto is located near Kanto, and the games allow players to return to Kanto after completing the Johto storyline. This was a notable continuation because it expanded the original adventure rather than replacing it with an entirely separate world.
The second generation added 100 new Pokémon, bringing the total species count to 251 at the time. It also introduced features such as Pokémon breeding, held items, a day-and-night cycle, and the Steel and Dark types. Kanto belongs to the first generation, Hoenn to the third, and Sinnoh to the fourth.