Regret had existed since time immemorial, since the first mind capable of reflecting upon its actions took a moment to consider the consequences of its decisions. With each passing generation, as minds more intelligent and wise came to be, so too did Regret become more and more powerful.
It was unfair to think that Regret was cold and uncaring; after all, it would be silly to think of an emotion as unemotional. As one subjected to the final misgivings of every living mind, she was audience to their suffering and their ultimate sorrow and defeat. Even though this was the very essence of what she was, the burden of grief bore down upon her until one day she found that she could not stand it any longer. Deciding to take action, she picked a random thread of thought and followed it back to the mind that had given it life.
The mind of a human was a turbulent thing at the best of times, but the panic that accompanied impending death made a fantastic mess of things. A torrential rush of clashing thoughts rushed through her as she reached out and touched it:

Why didn't he wait for the others to catch up?
Why didn't he watch where he was going more carefully?
If he had worked out just a little more, would he have been able free himself?
If he wasn't stuck, would he have been able to save just one more?
Would his family be alright without him?
Would—

With a jab of pain and a final shudder, the candle was snuffed out and his broken body lay still. Regret sat and stared for a long time, turning the thread in her hands over and over as she replayed those final thoughts. An eternity passed in the blink of an eye as she deliberated, but in the end she came to a decision: she of all people would not allow herself to have cause to have misgiving. Delicately, she reached out and re-lit the candle.

John gasped as he came to again, coughing violently as his lungs burned from the stifling smoke. In an act of desperation, he found one last reserve of strength and pulled himself out from under the pile of debris. With his equipment broken or missing and his eyes watering, he threw the unconscious child back over his shoulder and pushed on through the raging flames. Somehow, he managed to make it all the way back to the main entrance before his legs finally gave out. His last conscious thought was that everything would be alright as the paramedics rushed to his side and took the still-breathing child from his arms.
He woke up in the hospital two days later, and paid little attention to the doctor's bewildered inability to explain how he was still alive; he had more important things on his mind. Things like never forgetting to tell his wife he loved her again, not missing another one of his son's soccer games, and making sure that all the proper arrangements were made if something were to happen to him.
Three weeks later, John rushed to the site of another burning apartment building. The chief hesitated, and tried to explain to him that the building was too dangerous to enter, but the crying of a child over the roaring flames ended all further discussion. Without Regret, he turned and rushed through the door.

Shaking from the exertion, she knew instantly that she had irrevocably lost a part of herself as she sank to the ground. Yet, even as her eyes watered, Regret smiled, knowing that through her sacrifice she had given a man a second chance. Without hesitation, she drew another thread — the nearest she could find — and followed it with determination.
Time passed as she touched countless lives, selflessly giving a month, a week, a day, or even an hour, one extra chance after another to do that which they could not before the end. A young man recovering from a car accident finally found the courage to confess to the woman he loved. A mother who fell down her stairs told her daughter that despite everything that had come between them, she was proud of her accomplishments. A new father and survivor of a heart attack held his newborn son for the first time.
And then, the unthinkable happened. With an outcry of agony, the minds linked to her began to wink out, a catastrophe of global proportions. Millions, then billions, died, their flames extinguished in the blink of an eye. More would follow in the wake of the disaster, but despite the pain that threatened to cripple her, Regret continued to touch as many lives as she could, giving them the closure they so desired until but a single thread remained.

Was there more he could have done?
If he hadn't approved that last experiment, would none of this had happened?
If he hadn't been so ambitious and reckless, would he have been spared the torture of watching his friends, family, and coworkers suffer in the last waning hours of humanity?
Was this all his fault?

It was unfair to think that Regret was cold and uncaring. She had avoided interfering with the actions of those she touched, but she would make an exception for this last human man lying alone in the ruins of civilization. A part of her knew that this was it; with all minds gone, there would be no more reason for her to exist. So weak was she that she could not even fully re-light the candle; as its meek flame sputtered in the darkness, she took the man's hand in her own and, with a firm but gentle motion, traced his finger through the thick ash that covered the ground until a crudely formed phrase took shape:
It's okay. You did your best.
The flame went out one last time, and only the darkness remained. Regret closed her eyes with a final sigh and sank into nothingness.
But it was not the end.
Was there something left, something she had missed?
What part of her could possibly remain when no more existed?
Struggling against the emptiness, Regret reached out as far as she could, stretching up on tip-toes until her fingers brushed against a distant but unmistakable thread. Clawing at it with her final shred of strength, she latched on with all her might and pulled herself towards it.
Feeling warmth against her face, she opened her eyes to the brilliant green light of an unfamiliar sun.