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Tear Jerker: Star Trek Online
'Cloaked Intentions', the Featured Episode series focusing on the Romulans and Remans, has a couple of doozies.
In 'Mine Enemy', a Romulan miner talks about her life and the destruction of Romulus:
"My family and I have been here all of our lives. It's a hard life, but it is all I know.
My mother used to tell me tales of the homeworld. She'd talk about the plazas in Rateg, or vacations she spent with her father on the shores of the Apnex Sea. And she would tell me about my father, who gave up his place in the military evacuation ship so she could live. He ... he never knew he had a child.
She would tell me these stories, and later, when she thought I was asleep, she would cry."
In 'Frozen', the next mission in the story arc,we get to hear from the regular grunts of the Reman resistance... and it's not pretty. An example:
Player: Why are you fighting the Romulans?
Reman: My wife was working on a mining ship. This was not a military vessel. It had no weapons and limited shields. It was not in restricted space, and it threatened no one. The Tal Shiar captured it and "questioned" everyone on the crew for weeks. My wife died screaming in a Tal Shiar interrogation chamber. I fight for her.
Player: What do you want when this conflict ends?
Reman: What do I want? I cannot answer that question. All I wanted — all I will ever want — died with my wife.
The Cardassian mission 'Badlands', when you learn the fate of the parents of Joshua Riker.
In the mission "What Lies Beneath": When you find the latest victim of the crazy murderer, only seconds after she was begging for you to help her. AND once you realize the murderer was a hologram whose program degraded due to the radiation down there.
Most of the Romulan Captain's story arc. It starts off with your colony being invaded and it gets worse from there. The penultimate mission shows that just about everyone abducted was or is in the process of being turned into more Elachi.