This Ninetales is a fire-type Pokémon owned by Blue.
Blue caught Ninetales when he switched his Pokémon with Red. Red sent Machoke, who evolved into Machamp and attacked Ninetales. Blue caught it and kept it, responding to Red it was his Machamp that defeated it, though Red wanted it badly.
At the Indigo League, Blue sent Ninetales to fight Red's Poli and Pika, who jumped to the ceiling, as the floor was burning by its Fire Blast. Blue called Ninetales back, but did not know Red used strategy to condensate water from Poli and charge it up with Pikachu's electricity.