The Moonlit Princess

Speak to Seggin, who resides on the west bridge in the Zoras Domain. He will explain that he cannot forget the sight of Princess Mipha, holding her Lightscale Trident in the light of the moon. He wants to see that image of her just one more time. Once you've activated this quest, go up to Shatterback point, where the statue of Princess Mipha is. Timeskip to night and wait for the moon to be up in the sky, about halfway up. Take a picture of the statue, and it should indicate it is for the quest with a small speech bubble with an exclamation point, the words "Moonlit Princess Mipha". Return to Seggin, and show him the picture. He will gift you a decayed zora sword.