Please don't list this on a work's page as a trope. Examples can go on the work's YMMV tab.
Tear Jerker: Samurai Jack
Near the end of episode L (#50), when X9, now powering down, and dying, asks Jack to take care of Lulu. Cue Jack showing a worried expression at possibly killing a perfectly innocent robot.
Made all the more worse knowing that you, as a viewer, could predict the ending before it transpired. It was only a matter of time before Jack got the drop on X9 and slew him. What makes it worse? That it's a Deconstruction story told from the perspective of a random robotic mook who had a life and an existence up until he was took out by Jack for whom it was Tuesday. Imagine how many other bots before him lived.
"Lulu... sweet thing."
Jack's sword doesn't hurt the innocent. Either it saw X9 as guilty, or... it does not recognize machines.
Jack and Lava Monster features Jack fighting his way through a maze of death only to confront a near-invincible giant lava monster. Then we learn that the lava monster was actually a Viking warrior, imprisoned by Aku in solid stone. He learned to form the stone around him into a monstrous body, and can only be freed to enter Valhalla if defeated by another warrior in honorable combat. Which Jack does, sending the fallen Viking on to eternal rest.
I think you're referring to "Jack and the Monks.":
"Have you FORGOTTEN!!??"
Even the early parts of that episode are heart-wrenching. At a few points Jack just sounds so defeated.
"Jack Remembers the Past" is heartbreaking.
The worst part is when he sees his family crest on the bell, and he realizes where he is and starts crying.
Jack:(falls to his knees): my home...
"Jack and the Warrior Woman." Sure, most viewers were certain that Ikra was evil and was going to betray Jack, but that almost made it worse! The audience guessed it, Jack could have guessed it, he really should have known, but he was too sad, lonely, and kind to. Let that be repeated, in this story, a multi-episode Story Arc ends in the gut-wrenching defeat of the hero, because said hero was too sad, lonely and kind! And this was just the 6th episode!
"Jack and the Travelling Creatures". After the whole episode Jack had spent travelling, passing test after test to prove his worth, he finally stands before the real, genuine time portal. There is a guardian in front of it and Jack humbly asks to be allowed to use it and is denied. He sounds so jaded after he realizes that he has to fight yet again.
Jack: "I had hoped that just once, I would not have to battle for my goal, because it is noble and just. But I see that this is impossible."
After the guardian Curb Stomps him, he decides not to kill him after all. "You can't use it yet, Samurai Jack. Not yet... Not yet."
The ending of "Princess and the Bounty Hunters" was particularly heart-wrenching. Princess Mira, an Anti-Villain who's only some motivation to claim the bounty on Jack was so that she can free the oppressed people of her country, works hard the entire episode to set up a well-laid trap. In the end, Jack Curb Stomps the bounty hunters, only leaving her alive. When she realizes she can't defeat Jack, she drops her weapon and cries, solemnly accepting that she can never save her people. It's sad to see her so tragically accept this fate, even though Aku would probably not free her country anyway. What makes it worse is that Jack doesn't even acknowledge her presence or offer to help her, even though they could have easily been great allies or even friends. What makes this even more tear jerking is that, knowing Jack like we do, he would have gladly helped her without hesitation. All she had to do was ASK. But she's too filled with pride to do so.