This is based on opinion. Please don't list it on a work's trope example list.
Tear Jerker / Power Rangers Time Force
Nadira and Frax. Particularly the part where Frax is desperately pleading with Nadira to end the cycle of hatred as he gets dragged off to be reprogrammed. Big kudos to Eddie Frierson.
Frax's reaction when Nadira tries to ask him about being human, and he just spits at her.
Frax: You're an evil mutant with a heart as black as coal, just like your father. Now get out of my sight, you sicken me!
Everything that happens to Frax in the finale. But especially when he's dragged away, and realizes Nadira means what she says, and that things can change. And then Ransik has him lobotomized.
Dialogue here for your enjoyment
Nadira: "I'm SORRY... for what my father DID to you, Dr. Fericks
Frax:(shoves the Cyclobots aside, as he turns around, and exclaims in intense shock)WHAT?!
(Nadira smiles with pity and turns to leave, an image of Dr. Fericks, the man who Frax used to be appears on his chest gem)
Dr. Fericks: There's hope for her (the image vanishes)
Frax:(struggles with renewed strength, smacking aside a Cyclobot, and declares with all that's left of his spirit) Nadira! WAIT! Wait, I was WRONG! You DON'T have to hate! You can... You-you can break the cycle of hatred! NEVER give up! NEVER... ack! Never give UP...!
(Nadira had been walking away, but slowly turns around, and watches in visible trepidation as the Cyclobots assault Frax with their tasers. He whimpers in agony, but manages to finish his speech, while being harshly drug away by his former creations. Nadira appears appalled, but as unable to protest outside of a few small moans of sadness. Frax's final words echo distantly)
Frax: DON'T GIVE UP!
Frax's death. Gah. And the fact that Nadira's the only one who cares.
The scene where Wes faces that army of Cyclobots, alone. The music really sells it.
Wes saying good bye to the other Rangers. Especially Jen, after they each confess that they love each other. The only thing ruining that scene is that they don't kiss.
Jen meeting Wes for the first time. Her teary reaction and being stunned to silence at seeing an Identical Stranger that looks just like her recently deceased boyfriend was heartbreaking. Kudos to Erin Cahill for her performance.