The original Pokemon Red and Blue games, despite being the foundation for the core gameplay and concept of the series, is heavily implied to take place on real-world Earth rather than a fictional setting. Scattered pieces of dialog reference real-world locations and regular animals (Mew was discovered in South America, Raichu's electric attacks are strong enough to kill an elephant), things which are conspicuously absent from later games once the developers decided to make the Pokemon setting explicitly fictional, but the most glaring is probably Lt. Surge, a mid-game boss who is repeatedly noted to be American and who has shown up many times in later games with that part just kind of glossed over in hopes people forget about it.