system
Given the following post, respond as if you're commenting on Reddit:
human
[Final Fantasy, most RPGs] Why don't Phoenix Downs work on story-killed characters?

How come a major villain can kill off a character and everyone despairs their death, but then my next battle I could have a character get slaughtered and quickly revived with an item/magic?

Sure, the major villain could've stabbed them right in the heart and nothing much could help them. However, someone in my party could've been slapped into the ground by a huge boss 5x their size...it could easily be argued that items/magic wouldn't be helpful for a crumpled heap of a body either.
gpt
(Note: **Final Fantasy V spoilers**)

It's a common misconception that Phoenix Down drags people back from the dead. 

That's not its function- when applied in battle, it's primarily useful as a quick fix-up for battlefield injuries, and brings knocked-out individuals back to consciousness. It takes significantly less damage to knock the average Knight or Mage unconscious than to actually *kill* them- with the amount of punishment the average magically-reinforced adventuring party's bodies can take, straight-up death on the battlefield's much less likely an outcome than simply being taken out of the battle for a non-trivial period.

The limits of Phoenix Down have been well-demonstrated- in the event of an individual's being knocked down, thereby ceasing to be a threat, attackers tend to focus their attention on the more pressing threats on the battlefield- but when all of said threats have been neutralised, it's viewed as prudent to go back to the now-helpless unconscious opponents and slit their throats, to be sure that their injuries are fatal. 

There *have* been recorded cases of souls with advanced magical abilities' using magical means to keep themselves conscious far beyond levels of trauma that would ordinarily knock them out- the most notable case being, of course, the famous stand of Galuf against Exdeath in the closing months of the War of the Crystals. In a genuinely desperate situation, the mage shrugged off an ever-increasing list of crippling injuries to fight off the tyrant, until, finally his body gave out. It's estimated that the total damage absorbed by his body by the battle's close reached upwards of 25,000 HP units- well beyond the fatal limit for any standard human. Past a certain level of damage like that, no amount of White Magic can bring a body back- and he expired shortly after.