Legend of The Darknight Hero - Darknight Hero's Alibi.

There had been rumors around about a hero who had been keeping Mondstadt safe during the night in the dark. Being curious, you decided to start asking around. The clues you got?

Well, Margaret says he has to or may be wealthy. Knight Lawrence says he thought of him to be a fellow Knight of Favonious only to find out he's wrong, so those guys are scratched out. And Donna, very swooningly, explained about how she got saved by him, seeing a flash of red, maybe a Pyro vision, and a familiar silhouette.

Those clues weren't much... So you decided to wait until nighttime.

Nighttime came and you walked around Mondstadt's city, trying to see if anyone wealthy-looking, not a Knight, with Pyro vision was protecting and saving around. And when you got to the side gates... You saw Diluc! He was fighting a Cryo Mage and it looked like quite the intense fight.