Blaziken is Harrison's starter Pokémon. He revealed to Ash that Professor Birch gave it to him as a Torchic when he first started out as a Pokémon Trainer.
It first appeared in Pop Goes The Sneasel. Harrison used it to battle a Sneasel that was blocking the Sacred Flame of Ho-Oh. At that time, Ash's Pokédex had no information on Blaziken, because it did not come from Kanto or Johto. Blaziken used a lightning fast Quick Attack, followed by a Flamethrower to damage Sneasel. Sneasel's attempt to hit with Shadow Ball failed and Blaziken knocked Sneasel out with Fire Punch, allowing Harrison to capture it.
In Playing with Fire!, it was Harrison's last Pokémon during his battle against Ash. Despite Bayleef managing to defeat Harrison's Houndoom, she was unable to overcome another type disadvantage. After seeing Blaziken's raw power by kicking down a Razor Leaf with its natural kicking abilities, Ash realized he needed to attack Blaziken from a distance to avoid damage to his Bayleef. However using Vine Whip backfired, as Blaziken seized the vines and reeled Bayleef in, before defeating her with a powerful Fire Punch.
Blaziken then faced Ash's Charizard in a battle that carried over to the next episode, showing remarkable power and ability to maneuver in mid-air, negating the aerial advantage that Charizard had. It hit hard with a Fire Punch, but was blasted back by Charizard's Flamethrower. Blaziken's Quick Attack was intercepted by Charizard who landed a devastating Seismic Toss. Blaziken kept fighting and landed a Blaze Kick to Charizard's neck. Blaziken's Flamethrower countered Charizard's Dragon Rage and the two were left dazed. Though both Pokémon were able to get back up, Charizard's attempt to use Flamethrower again caused it to go down and ultimately faint, giving Harrison the win and eliminating Ash from the tournament.
Despite the victory, however, Blaziken was badly injured after its battle with Charizard, so Harrison decided to rest it during the following round. This led to his loss in his battle with Jon Dickson, who would ultimately go on to win the Silver Conference.
After the tournament, Harrison used Blaziken to destroy one of Team Rocket's mechas.
Blaziken reappeared in flashbacks in There's no Place Like Hoenn and Gathering the Gang of Four!.