Astro's First Love is episode 52 and the final episode of the 1980's Astro Boy series.
Summary[]
Osamu Tezuka reveals a secret about Astro Boy: his legs are those of a robot girl. He says that the episode will focus on this backstory.
Astro is tasked to retrieve one of his own blueprint templates from a military fortress of the Grota Republic. He meets and bonds with Niki, a sentient robot girl built from his very template, which unfortunately incorporates a neutron bomb. In order to stop the bomb, the two robot children have to make a costly sacrifice: she must be completely dismantled in order to stop the bomb. All that is left of her are her legs, which Astro takes to Dr. Elefun and asks him to switch his legs with hers, so that she could be a part of him forever. Astro tells the viewers not to tell anyone about their secret and wishes them bye as he flies away.