Shadow knew that Pluto's Kokoro would become a weakness, so he made a duplicate of him while fighting Astro. While Pluto was just about to destroy Astro, he stopped, because of his Kokoro. So Shadow sent Acheron, however Pluto sacrificed himself in order to save Astro. Shadow later commented "Kokoro isn't a weakness, it makes robots stronger".
The 2003 series was his only appearance.