"The Secret of the Egyptian Conspirators" was basically an extended Pet the Dog moment for Dr. Tenma, from saving Astro to trying to help his would-be assassin Cleopatra.
Tenma's reasoning behind helping Astro to fight Pluto. "I did it because I love him, and didn't want to see him destroyed!"
Professor Ochanomizu's unwavering belief in Astro when he goes bad. He states himself he won't give up on him.
In Volume 20, Tenma accepts that he no longer has the right to call himself Astro's father, and tells Astro's robot parents that he knows they'll make him happy. He then leaves and gets attacked by a man he had previously betrayed. Astro Boy saves him without hesitation.
Tenma finally gets his act together and teams with Elefun to slight-of-hand the Blue Core out of President Stone's grasp so he can use it to revive Astro. Tenma embraces Astro, telling them that while Astro is not Toby he is still Tenma's son, and then urges him to escape while Tenma and Elefun stay to face down the military.
In the denouement, when Tenma embraces Astro in relief on realizing he's not dead. The warmth between these characters in the third act, while a departure from their previous dynamic, is incredibly sweet.
Also in the denouement, Zog "resurrecting" Astro/Toby by using some of the Blue Core energy that Toby had used to restore Zog.