In order for Yuria 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 place in Firelink Shrine, they will find him already dead with Yuria standing close by.
Upon introducing herself, Yuria reveals that Yoel was a close friend to her and thanks the Champion of Ash for allowing him to be redeemed through his actions while at their service. She then does the same, pledging allegiance to the player 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.
Once Orbeck of Vinheim has moved to Firelink Shrine, Yuria will alert the player that he is he has proclaimed himself to be "Lord of Hollows," asking the player to settle the matter lest he imperil the player's rule. If the player brings Orbeck's Ashes to Yuria, she will reward them with the Morion Blade.
Once the player reaches the Catacombs of Carthus, Yuria reveals that she is also guiding Anri of Astora along the path to Irithyll of the Boreal Valley, and plans to engage him/her (gender is always the opposite of the player's) in matrimony. To this end, the player must aid Anri and keep him/her alive up until Pontiff Sulyvahn has been defeated (care must be taken not to kill the Londor Pilgrim within the Church of Yorshka). If successful, Anri may be found in the old Darkmoon tomb, Dark Sun Gwyndolin's boss arena in Dark Souls, and can be "married" here, gaining 3 more Dark Sigils for a total of 8.
Once the player completes their wedding vows, Yuria will swear her fealty to the true Lord of Hollows. She will no longer become aggressive if attacked by the player, short of the Dark Sigils being healed by the Fire Keeper. She will also make herself available to be summoned for the Soul of Cinder fight. Should she be summoned and survive this fight, her set and weapon can be found at her usual spot at Firelink Shrine.
If Yoel dies before the player can attain all five Dark Sigils, Yuria will not appear and the Londor Pale Shade will invade in the Farron Keep and Irithyll of the Boreal Valley; the Pale Shade will also invade the player at these locations should Yuria be killed or angered. Defeating the Pale Shade once will reward the Manikin Claws, while defeating them at both locations will cause the Pale Shade Set to appear at Firelink Shrine in the same area where Yuria and Yoel used to reside.
Conversely, if the player has not turned Yuria hostile, the Londor Pale Shade will become available for summoning in the aforementioned areas.
Yuria will disappear if Anri dies at any point before Pontiff Sulyvahn.
Yuria possesses additional dialogue should the player progress through the Painted World of Ariandel. After talking to Sister Friede and returning to Firelink Shrine, Yuria will recognize the scent of her sister, and warn the Ashen One of heeding their kindness over their principles.
Once Sister Friede has been defeated and the player in possession of her soul, Yuria will remark on Elfriede's history with Londor, and request that the Ashen One usurp the First Flame in her memory.
Should the player have not yet acquired 8 Dark Sigils in either case, the dialogue will vary slightly.
"...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."
About 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."
After performing the ritual with Anri of Astora
"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 Old Woman of Londor
"Thou'st forsworn the Lord's Mark. There is naught more to say. Farewell, our fleeting Lord."
After reaching the Kiln of the First Flame
"Ahh, our Lord and Liege. Thine heart is fix'd upon the linking of the fire. But, brave usurper, I prithee, wrest the flame from its mantle. So that we Hollows, in most honest shape of man, may have it for our own."
"Honourable usurper, I prithee wrest the flame from its mantle. So that we Hollows, in most honest shape of man, may have it for our own."
Attacking her with five Dark Sigils
"Where are thy wits?"
"Cease this at once!"
Making her hostile
"Hmph, Yoel knows not of thy folly. A Hollow need not be mad. No one so weak shall ever rule us!"
Upon killing the player
"Peasant, at least thy cadaver shall a little kindling make...."
"Kaathe, I have failed thee..."
Attacking her while in possession of eight Dark Sigils
"Thy Lordship, what is the matter?"
Killing her while in possession of eight Dark Sigils
"Brave usurper, I beseech thee claim the fire..."
After meeting Sister Friede, with five Dark Sigils
"Ahh... thy scent seems most familiar. A sweet fragrance long faded from our own bosoms. How this came to pass I know not, but... Take heed, kindness can wear upon one's principles."
After meeting Sister Friede, with eight Dark Sigils
"Ahh... our Lord and Rightful Liege... thy scent seemeth most familiar. A sweet fragrance long faded from our own bosoms. My Lord, how this came to pass I know not, but... Take heed, kindness can wear upon one's principles."
In possession of Soul of Sister Friede, with five Dark Sigils
"Might that soul be...? Nay. Never mind. It belongs to a woman from Londor. To provide succour for the Lord of Hollows surely would bring her much honour. In return, thou needst only do her a small kindness... Remember those who stayed by her to the end, in the shadows cast by fire..."
In possession of Soul of Sister Friede, with eight Dark Sigils
"Ahh, our Lord and Liege. 'Twas the soul of my sister. Elfriede... a poor wench turned to ash, who would abandon Londor. If thou wouldst, let it nourish thy Lordship, and in return, do her a small kindness... Remember those who stayed by her to the end, in the shadows cast by fire... And lastly, my Lord, take up thy rightful mantle of Usurper."
Yuria will leave Firelink Shrine if the player talks to her after healing their accumulated Dark Sigil. If the player does not engage in dialogue with her after healing their Dark Sigils, Yuria will remain in Firelink Shrine indefinitely, though this serves no practical purpose.
Yuria only drops her ashes if the player kills her. As such, defeating the Soul of Cinder will mean that her wares are no longer available, unless she is killed before she has a chance to leave.