Dolores: AI. Artificial intelligence, but in Japanese it means "Love"...
The first game has a bad ending that's really hard to achieve by normal means unless you go out of your way to do so, but definitely qualifies as a Tear Jerker nonetheless. Fail all the SOS missions, and Thunderheart will be brutally and abruptly killed by an explosion as he's talking to Leo. ADA will confirm that what caused the explosion was Jehuty destroying the colony shaft; in doing so, it hit one of the colony's underground lifelines. Cut to a grim The End screen, with a destroyed city in the background, and the game returning to the title screen. ADA's Brutal Honesty and Leo's reaction set the deal, as ADA doesn't just sound like she's berating Leo; she also sounds like she's berating you, the player, for screwing up this badly, if not outright going out of your way to cause this.
ADA: In other words, you killed him.
Leo: But, I didn't mean... *cut to the The End screen*