From Bulbapedia, the community-driven Pokémon encyclopedia.
Koji was the Character of the day in Good 'Quil Hunting. He was a brash young trainer trainer who wanted a Cyndaquil and ended up competing with Ash to catch one in a forest. Even though Ash caught one first, Koji goaded Ash into a battle with the prize being the Cyndaquil Ash already captured. Against Brock's better judgement, Ash accepts the challenge and has Cyndaquil do battle with Sandslash. Despite having a disadvantage, Cyndaquil is a able to use its speed and Tackle attack to defeat Koji's Sandslash. Koji then decided to try to steal Cyndaquil anyway, only to get badly burned with it spat out a Flamethrower at him, causing him to run away crying.