At the opening area after being eaten by the Titan Uraya, there's a side-quest that can be initiated in the lower area right in front of you. You'll have to progress the main story while tackling the various points of this quest, but it does have an interesting payoff.
Instead of going directly toward the main quest objective on the upper level in the Titan Uriya, go to the area below after moving ahead. You’ll want to draw the monsters out one by one because they’re fairly tough but, once you do, grab the item to the right. It will start the quest “Mysterious Note” which guides you to a location marked on the map inside Uraya.
The point is on a raised platform that you'll come across and you’ll only be able to reach the marked spot by riding down a tunnel from here:
You'll have to time your jump perfectly near the end so that you launch your character to the raised platform. It may take a couple tries, but you can fast-travel back up to the top if you miss your mark.
Once you arrive, you’ll find two treasure chests and will experience a cutscene where you’ll find a broken knife. One chest will have already been opened and you must search for the person that used the knife to open the chest.
The Knife's Owner
You’ll have to advance the main quests a bit to access to next area, which is in Uraya’s stomach. There, you’ll find Erebos, the owner of the knife. After a miscommunication, you’ll have to fight and defeat him. Afterward, talk to him again to finish the quest.
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