!!! ''Original Manga'''
* Hoshie's death.
* Tenma ''finally'' giving up on his schemes to reclaim Astro as his son: "I'm sorry... I give up... I just wanted Astro back, that's all... I thought if I could get a brand-new Astro, he could be my son again... [[spoiler: so I tried to use Meeva to bring me a ''new'' Astro from the past...]] I know it was a crazy thing to do... but when I learned I couldn't have a brand-new Astro, I thought maybe I could get you to let me have the old one... I'm sorry... I know it's not possible... you win... I know you're his real mom and dad now... you're both wonderful parents... I know you can make him happy... I'll never come here again... I promise... give my regards to Astro..."
!!! ''1963 anime''
* Dr. Tenma/Boyton's reaction to his son's death... the worst being when we cut to him in his office, sobbing into his desk...
** And then later on in the episode is his rejection of Astro. Goes from saying he'll teach his son how to fly and jump mountains to ordering him angrily to get out.
* From ''Snow Lion'': "This is how it ends: in the snow. If it's the last thing I do, I'll put Astro Boy in the Robot Hall of Fame. Yes, Astro Boy, you've earned your place here with the best and here you'll stay for eternity... and here I'll wait for you, my friend. We'll face the end together."
!!! ''1980 anime''
* Tenma's desperate search for Astro in the second episode. Curse you, Hamegg!
-->'''Tenma:''' ''(calling for him)'' Tobio, I'm sorry. You are my child.
-->'''Astro:''' ''(trapped in a suitcase)'' Father... I'm here... Help me...''(slips into unconsciousness)''
* Nuka literally falling apart in Astro's hands.
* Atlas' HeroicSacrifice. His life was a hard one, with Lidian as his only real joy and who ultimately couldn't bear to be apart from him either. So they just... stand there holding each other contentedly while waiting for the end, leaving Astro to feel his brother die over their link...
!!! ''2003 series''
* Atlas' death five episodes into the series, though he later is rebuilt.
* Pluto's HeroicSacrifice where he drags a mindless clone of himself into a volcano to prevent him from harming Astro and Zoran.
* Astro's heartfelt speech to the Blue Knight about wanting humans and robots to live in harmony, with just about every character in the show watching via television.
* Astro's 'death', short as it may last. [[spoiler: Especially Tenma's PleaseDontLeaveMe]]
* The hug between [[spoiler: Astro and Tenma]] in the final episode.
!!! ''2009 film''
* [[spoiler:To anyone that read the original or knows anything about Astro's creation will see this coming as soon as Toby appears. Toby dies. Toby get resurrected by Tenma into Astro. Astro doesn't act like Toby that much. Tenma disowns him.]] It's the thing you expect the writers to have just glossed over... gets fully shown...
** Granted, they completely changed Toby's cause of death (he gets hit by a car in both the manga and some of the adaptations), but it otherwise might have been too scary for kids.
*** May have been MeaningfulEcho, given the climax of the film.
*** There's also a remote possibility that Toby was absorbed by the Peacekeeper. I was somewhat expecting that as a kid-friendly ending.
** The aforementioned PleaseWakeUp scene also brings tears.
** Tenma's collapse after [[spoiler: Astro's heroic sacrifice. Just when Tenma realized how much he really did love his robot son....]]
* When Tenma disowns Astro. This is mostly because of a truly harsh line delivered in a rather unique fashion. "And I dont... want you anymore." Somehow, Tenma manages to both sound just a bit confusingly relieved... and absolutely horrified that he's thinking this way. Even to those who know it's coming, the line is INSANELY cruel.