Otoshi is a Pokémon Trainer that met Ash and his friends on their way to the Indigo Plateau. His main Pokémon is a Marowak. After battling with Ash, he admits the badges he had earned were stolen. Because of this, his Marowak leaves him in frustration, because after all of the hard work attaining the badges; they now have nothing to show for it. After some detective work, Ash & Co. and Otoshi figure out that the thieves are Team Rocket and after Marowak returns and a little battling, Otoshi finally gets his badges back.
Otoshi's Doduo is used against Team Rocket in an attempt to get back Otoshi's stolen badges. However, it does quite bad in the battle against Jessie's Arbok and barely escapes being captured by Jessie when Otoshi's Marowak's Bonemerang attack knocks the Poké Ball out of the way.
Otoshi's Marowak is used in a battle against Ash's Bulbasaur and Pikachu. However, after defeating Bulbasaur, it is quickly defeated by Pikachu. After realising that all of its hard work earning the badges was lost after Otoshi's were stolen, it left him. It eventually came back after thinking about the training it went through with Otoshi and saved the day from Team Rocket.