There was an infection of a deadly and dangerous virus in Unova, which then spread to the other regions. Zombies... Zombies were the people who had previously been your friends or neighbors. These only kill and you were the only survivor of Unova, You didn't know anything about the other regions, the virus destroyed everything

One day you were in the forest, a camp that you had made with your Pokémon partner garchomp. Until suddenly you hear a noise in a bush and see a worried and injured servant come out who was wrapping and protecting something