Prologue:
One late afternoon, two children were playing in a public playground when one of them notices something directly above them.
"Hey, look! It has big wings!"
"Yeah! It looks like an angel!"
Then, another one appears, this time, with black wings.
"Look, it's another one!" the little boy points.
Above them, the two entities charged at each other. The two fought as black and white feathers fell on the two children like snow.
"It's beautiful!" the little girl said as she caught a white feather.
"Well, yeah."
Suddenly, the two winged beings started to dive towards them. In a desperate attempt to win, the black winged being grabbed the other and dived downwards at more than twice the speed of sound. They both crashed between the two children, sending them flying a few meters away from the site of impact. On its final act, the black winged being destroyed itself, taking the white-winged with him. A few minutes later, authorities came to investigate the explosion which they thought was a terrorist attack. Instead of finding remains of a bomb, they found a crater about ten meters wide and the two children a few meters outside the crater's rim, opposite to each other. The two children were seriously injured and sustained quite a lot of third degree burns. They were brought to the nearest hospital. When they were brought to the emergency room, the doctors said that they could do nothing and even the most advanced technology could only extend their lives for less than a week, until they eventually perish.