Astro Boy: Tetsuwan Atom - episode 4 - 26 Apr, 2003

Atom starts to go to school and makes friends with kids named Kenichi, Tamao, and Shibugaki. By chance, he also becomes friends with a mysterious robot named Lightning, who can disappear. The five of them deepen their friendship by playing with a sailboat. However, Lightning turns out to be a thief controlled by the villainous Skunk Kusai. When Atom and his friends realize this, they try to stop Lightning from doing evil deeds. (Source: Wikipedia)