Ninjask was shown being captured in a flashback, only minutes before Paul captured Chimchar.
Paul used Ninjask to battle Ash and his Gliscor in the Sinnoh League. Using its incredible speed, which was augmented by Agility and its special ability, Speed Boost, Ninjask dodged Gliscor's Stone Edge. It then used Fury Cutter to strike Gliscor, while evading its Fire Fang. Repeating its attack, Ninjask toppled Gliscor to the ground, causing it to become poisoned from Toxic Spikes placed on the field. Ash swapped Gliscor with Infernape, who used Flare Blitz. The attack hurt Ninjask a bit, but the move was intended to clear Toxic Spikes from the field. Ninjask then used Giga Drain, absorbing Infernape's energy, but was knocked out with Infernape's Mach Punch.
To mark its defeat in the battle, Ninjask's picture was blackened out on the scoreboard.