Pokémon Decay is supposed to be a best of the first four generations. It's intended to give the player as much nostalgia as possible by referring to the storylines of the old games. Due to natural disasters the four regions Kanto, Johto, Hoenn and Sinnoh collided and became one big Region, the Talem Region. The player wakes up and can't remember what happened. He has to find out what caused those natural disasters.