Disclaimer: I do not own Fairy Tail and collect no proceeds from these scribbles.
The Difference
He tried not to think about it too much, that minute-long vision of the future-that-would-have-been. Because he didn't understand. He couldn't explain why he had died. Hadn't he learned that the answer is never to sacrifice himself? When the entire world was in danger, all he had to do was remember his nakama to know that he had to live for them instead of dying for them.
So why did he die for Juvia?
Was she more important than the bonds he shared with his friends? More important than the fate of the world?
A minute. That's all he had, and that's all it took to flip the greatest lesson in camaraderie he'd ever learned right on its head. And it wasn't even the end of the fight. Whether Juvia died or he did, the dragon would live. There were still more dragons. There was no guarantee either of them would make it out alive. So why sacrifice himself for her when he knew he shouldn't give his life even to end the fight?
Because this was Juvia. And she was in immediate danger. Not the "If I don't stop this guy, something bad will happen eventually" kind of danger. The "She will die now and then how will I keep fighting" kind.
And it wasn't a case of "I can't win this battle unless I take myself out too." He could have warned her, like Lyon had. He could have pulled her out of the way instead of using himself as a shield. She was standing between him and the dragon, well within arm's reach. It might even have been quicker. He could have gone down with her as he had when it had been her and Meredy in harm's way a minute before. He could have hoped she'd get by on her own strength and avenged her death if she hadn't. He knew that. Now. But then... where had his reason gone?
So yes, for a split second that made up a significant fraction of a single minute, he had lost all reason.
And as he'd hovered above the battlefield, no longer a part of the action for those last seconds, he had seen her face. It was shock. It was anguish. And he never wanted her to make that face again. He had heard her voice, his name sounding like it was ripping her throat to shreds on its way out. Without the -sama.
So when the time came once more that he had to consider the weight of his life against that of his opponent, her smiling face, her voice calling him "Gray-sama," her the way her wanted her to always be, is what tipped the scales for life.