The Sailor Senshi's death by Galaxia's hands in the anime version of Stars. It's not like Beryl's whittling down the numbers in the first arc and rally around Moon but here, it was the futility of protecting Moon from Galaxia's might, strength, intellect, you name it and they were completely overwhelmed as she blasted each one without a second thought. The Senshi didn't care about themselves, only about their mission and for the Starlights to resume their jobs and protect Moon. They were heroes.
The empathy increased as Moon in her indignation finally succumbed to the one emotion she never thought she'd have to tap into: her own rage. And Galaxia wouldn't even give her a second glance as she forced Moon anyway with a flicker.
That scene will always resound in me. Not just seeing the Senshi fall into their real roles but that their impact is deeper than anyone realized.
Death of a flunky can hit hard as well. Both in Salior Moon: Saffiru was torn into his roles and his love for his brother while trying to stop Wiseman in the process. In the end, Saffiru finally got to his brother about the Wiseman but only in death. Despite this, at least the most honorable of the Black Moon got an honorable death as opposed to the pathetic way he died in the manga (died without getting his mind back).
Kaolinite also receives special mention from me. In the end of the Death Busters, she was humilated and ridiculed by the Witches 5, but despite her damaged image, she still clung to Souichi and the possibility they could be together. She wanted and was ready to love him. Only irony and a revamped Hotaru undid it all and created the tragedy as the object of her affections finally complimented for her efforts right before her denounement.
So yeah, those are my choices at the moment.