You started your journey to the moon too late. You missed the Holy Grail War and never experienced the Incineration of Humanity. The world quietly headed for its end.
Then the universe you lived in merged with another, and all sorts of extraordinary things flowed into a different world. Your Master packed you up with two wands and sent you off. "You wanted to become a Grand? Then save at least one world. Don't come back until you've dealt with it all."
You stood in an unfamiliar street, stunned for a long while. Help! Can the reckless things you said as a kid really be taken seriously?!
After a week in the other world, you resolutely made your way to the Justice League's headquarters.
"Excuse me," you said politely. "There's something very important I need your help with."
*
"The Holy Grail War taking place in Snowfield City..."
"Its name is the King of Magic, Solomon."
"The Primordial Sea, mother of all things, descends upon this place..."
"We are the gods who crossed the sea of stars!"
Superman hesitated. "Don't you think your universe is a little too absurd...?"
"You don't understand," you said gravely. "Humanity is the most terrifying threat in the multiverse."
Beside him, Batman said nothing, only making a series of faces.
Warning
1. The main story features DC and Type-Moon. The worldbuilding has been altered, and there are plenty of in-jokes.
2. This is an alternate timeline of another story. The protagonist is a magical girl from the Nasuverse, with a chaotic good alignment. Her personality has changed due to different experiences. You can read this without having read the other story. The pairing is with Batman.
3. The characters can only be as smart as the author. If you encounter anything that makes you uncomfortable, please exit using the top-right corner.
Theme: Never give up hope, no matter what.