Dove, the Unknown Martyr

"We owe her our lives, and yet we don't know her at all."

Powers are fragments of truths from beyond this world. Someone pushed beyond all their limits will occasionally have a flash of insight which is swiftly forgotten, gaining powers soon after. They first emerged in the late 1400s, weak and rare at first but gradually increasing in strength and frequency over the centuries. In 1914, global tensions reached a tipping point. Fueled by abilities beyond mortal ken, the battles of nations and empires engulfed the earth.
Years passed. Governments around the world, grasping for every advantage they could, began experimenting with powers in search of increasingly destructive combinations. The world might have burned before, but these new synergistic units threatened to break it.
Then the Unknown Martyr emerged, and pulled the world back from eternal war.

Summary

It could have happened anywhere in the world. By that time, almost no countries were still neutral in what had come to be known as the Great War.
The key components are these. A civilian, male or female, is born in the most difficult time of the War and grows up knowing nothing else. Yet they maintain their fundamental kindness and innocence, always eager to help anyone in need.
Circumstances conspire to bring them in contact with battle, or at least its aftermath. They start towards the injured soldiers they see, wanting to get them to safety or medical attention, or to make their final moments relatively painless.
One way or another, they die.
One way or another, enlightenment whites out the pain in their own final moments. They rise and reach out, refusing to fight yet determined to stop the war.
They always call themselves Dove.

Historical Basis

On July 17th 1939, everyone involved in the war experienced a great feeling that someone had died. Many had died in the fifteen years since the start of what had come to be known as the Great War, but never had they known with such bone-deep certainty that a death had occurred as a result of their fighting. In the wake of what followed, all countries involved agreed to armistice and an eventual peace treaty. By the time the last soldiers came home, the phenomenon stopped. Beyond that, the details vary. Although different countries reported different occurrences related to Dove, the vast majority agreed on her personality and appearance. Those with more presence of mind came back with matching details they noticed and corroborating evidence from questions they asked. These have been used to trace the likeliest person Dove could have been.
Sophie Girault was born in Rouen in 1921, seven years after the start of the Great War. By all accounts she was as innocent and kind as the stories portrayed her. Two days before her 18th birthday, the same day Dove appeared to armies the world over, she disappeared on her way to a nearby military hospital to see her father, who had been injured in a skirmish the day before.
Despite this, Dove remains the Unknown Martyr for the following reasons. Though Sophie often volunteered at that hospital, Dove would later display medical expertise which she would've had no way of possessing, to say nothing of her specialized knowledge of topics such as powers and geography. More worryingly, when shown a side-by-side comparison of Dove and Sophie, despite their identical appearances, Sophie's mother did not recognize Dove as her daughter.

Spread

Due to the global nature of the Dove phenomenon, their myth is common knowledge throughout practically all of the world. The Great War is taught in high schools or their educational equivalents, and Dove is always covered as a matter of course. Teachers are always careful to note that ceasefire would have eventually been reached without them.
Despite this insistence, Armistice Day is still celebrated in many countries, and white poppies are planted or worn in Dove's honor.

Variations & Mutation

The story of Dove has many variations, in large part due to the fact that they manifested differently in different countries. Much of Europe saw a young woman matching Sophie Girault's age and appearance, dressed in white and adorned with poppies. Russia and China, however, saw a boy with red eyes and arms wrapped in bandages. In contrast to the above, Japan reported no vision at all, only a voice of indeterminate gender in a gentle rainstorm. All other countries experienced any of these three at random, with no regard for alliances or ethnic backgrounds.
The first source of variation in the different stories about Dove center around how exactly they came to be martyred in the first place. An injured father (or brother, or uncle) in hospital, a childhood friend abandoned and dying in a lonely field, simple empathy for those left behind as lost causes; always a perverse reward for showing kindness and concern.
The second, far bigger source of variation is in what Dove did to enforce peace. This was not helped by the different groups around the world who piggybacked on the Martyr legend to carry out their own plans for the same. In some tellings, white poppies choke the weapons and windpipes of anyone who tried to launch ambushes in the enforced ceasefire; most others limit her intervention to forced sleep or unusually persuasive talking. It is commonly believed that the more violent or disconcerting responses were from those other groups.