In order for her to appear, the player must draw out their true strength (level up) with Yoel and acquire all five Dark Sigils before reaching the Catacombs of Carthus. The next time the player visits Yoel's usual residing spot in Firelink Shrine, they will find him already dead while a dark figure observes from the shadows.
Upon presenting herself, Yuria reveals that Yoel was a most precious friend to her and thanks the Champion of Ash for allowing him to be redeemed through his actions while at their service, at which point she does the same, pledging allegiance to them and accepting them as her Lord and of all the hollows in Londor, in the hope that one day the Ashen One brings back its glory to the world.
Upon talking to her, the player will learn the "Dignified Bow" gesture and afterward she will inform about Orbeck of Vinheim causing much consternation among her people, as he has proclaimed himself to be "Lord of Hollows", asking the player if they can see into this matter. If the player kills Orbeck and brings back his ashes to her, she will bestow them the Morion Blade.
If the player completes Yuria's questline and "marries" Anri of Astora (and does not turn Yuria hostile anytime by either killing Yoel or by healing the Dark Sigil before the ceremony is complete), she will become available to summon for the final battle. If Yuria survives the encounter with the Soul of Cinder, her armor set and weapon will become available at Firelink Shrine.
"...Oh, prithee...art thou good Yoel's master? I am Yuria of Londor, a close friend of his.
Thanks to thee, Yoel's soul is redeem'd. Allow me to express my gratitude, in his stead.
Another matter. Thou'rt a Lord, art thou not? Bearer of the dark sigil, and our Lord of Hollows. For the time thou remain'st our Lord, we of Londor shall serve thee. And I, of course, am also thine."
Orbeck of Vinheim
"Oh, good Hollow. I'm afraid I must say... Orbeck of Vinheim is a cause of much consternation. He proclaimeth himself Lord of Hollows. If left alone, he may one day imperil thy rule. Fall to this matter yarely, else we are unravelled. Decisiveness is the mark of a true monarch..."
Giving her Orbeck's Ashes
"Ahh, I see Orbeck's claim is proven false. As it should be, our right and deserving Lord of Hollows. It is a Londor treasure, befitting of a true Lord. Lord of Hollows, may the dark sigil guide thy way."
After talking with Anri of Astora in the Catacombs of Carthus
"Our Lord and Liege. Knowest thou of a youth/maid named Anri? He/She is hollow, and will join thee in wedlock. A fellow of mine guides him/her at this moment. When the time is ripe, thou mayst make thy salutations. For what Lord taketh no spouse?"
After defeating Pontiff Sulyvahn
"Ahh, greetings, our Lord and Liege. Good tidings.Thy spouse is ready. The time is ripe to greet him/her. The boy/girl awaits thee, in the hidden Darkmoon chamber of Anor Londo. So thou mayst a true monarch become.
When performing the rite with Anri
"Ahh, our Lord and liege. I presume thy holy vows are sworn? Wonderful. Now thou'rt the true and deserving Lord of Hollows. With a spouse, the strength to claim the fire is thine. Thy Lordship, I prithee wrest the fire from its mantle. I, Yuria, and all of Londor, embrace thy impending Lordship."
"Our Lord and Liege. I prithee play the usurper. When the moment cometh to link the fire, wrest it from its mantle. The Age of Fire was founded by the old gods, sustained by the linking of the fire. But the old gods are no more, and the all-powerful fire deserveth a new heir. Our Lord of Hollows, it shall be, who weareth the true face of mankind."
After healing the Dark Sigil
"You have healed the Lord's Sign, there is nothing to converse about..."
After killing the Pilgrim following Anri
"Thou'st forsworn the Lord's Mark. There is naught more to say. Farewell, our fleeting Lord."
"Where are thy wits?"
"Cease this at once!"
Attacking after Usurpation of Fire ending
"Thy Lordship, what is the matter?"
"Brave usurper, I beseech thee claim the fire..."
Making her aggressive
"Hmph, Yoel knows not of thy folly. A Hollow need not be mad. No one so weak shall ever rule us!"
She kills the player
"Peasant, at least thy cadaver shall a little kindling make...."