FFVII's main antagonist Sephiroth was the son of two scientists who decided to start screwing around with magic, ancient demon DNA, and their own reproductive organs. The results worked out... actually better than you would think for a long time. Eventually, though, Sephiroth found out about his origin, went cuckoo for Cocoa Puffs, and a looming planetary Armageddon was initiated.
His mother Lucretia is a very minor character in the story, but she is still alive in some form. She can even be found by carefully maneuvering the submarine to surface in an isolated lagoon. Once there, though, you'll get nothing of importance from her unless you also have the man who was in love with her, optional character Vincent Valentine, in your party.
Assuming you recruited Vincent and found the hard to reach lagoon, and know enough to look behind a waterfall (All gamers do, of course), Lucretia will recount the sad love triangle that ended with her child turned into an experiment, herself altered forever, and Vincent becoming a strange vampiric creature.
She will also ask Vincent about her son, and Vincent, who is otherwise a cold and emotionless character throughout the game, tells her that Sephiroth died rather than burden her with the evils he has committed. It's a desolate, lonely sequence that is among the most moving in the game. It's not the best though.
Aeris' death scene is one of the most famous in all the Final Fantasy games. Depending on which characters are in your party they will react in different ways. Here's the problem.
To see those reactions you have to save before the scene, then fight a big boss battle, then reset and change party members if you want to experience them all. That's a big pain in the ass, and most people aren't going to go to the bother. Besides, the character's reactions aren't all that great anyway. They don't even have any lines...
Except for Yuffie's. Yuffie, as a young, cocky, teenage ninja is another FFVII optional character, and harder to recruit than Vincent to boot. You may not even have her around by the time Aeris eats it. If you do, though, and she's in your party when you fight Jenova-LIFE, you'll get a fantastic scene.
Yuffie looks at Aeris' body and walks to Cloud. At first her sobs are small, but soon she can't even hold herself up and collapses into his arms in a pure, mournful release. It's the only time in the entire game she shows any emotion beside youthful anger and excitement. She completely opens herself at the death of her friend, and unless you have the right party you'll miss it.
