“May you be the truest Lord, of Londor yet”. To start Yuria’s quest, you want to be in the Undead Settlement early playthrough, to bring Yoel back to Firelink before you reach the Catacombs of Carthus. You need 5 Dark Sigils in your inventory for Yuria to appear at Firelink. Each level up with Yoel, you gain a Dark Sigil. Dark Sigils bring you closer to hollowing upon each death. Every time you die, the number of Sigils in your inventory will be the number added to your hollowing meter. Once Yoel is at Firelink, speak to him and draw out your true strength to gain a Dark Sigil. After this, you will need to die a total of 9 times to gain 15 hollowing, allowing Yoel to give you 4 more Dark Sigils and levels. (It is optional, but make sure your Intelligence is at 10 here). After you have acquired 5 Dark Sigils, save and quit, and Yuria will appear beyond Yoel… Talk to her. Now… at this point, you have 2 choices. You can heal the Dark Sigils to become human again, consequently cancelling Yuria’s quest for this playthrough, by giving the Firekeeper Soul to the Firekeeper and paying for ALL the levels you spent on Yoel…
Or… You can continue on with Yuria’s quest to become… The Lord of Hollows. If you chose the latter, then the next step will be in the Road of Sacrifices. Exhaust Anri’s dialogue, and while you are here, with 10 Intelligence, Bring Orbeck back to Firelink for an optional quest that Yuria gives you, In which his ashes are needed either by progressing his quest to the Grand Archives… Or by killing him. If you have acquired Orbecks ashes under ANY circumstance, bring them to Yuria, and she will award you with the Morion Blade. Next, Progress Anri’s quest up to the Catacombs, and tell Anri you have not seen Horace at both spots Anri will be standing. Then, Head to the Smouldering Lake, to kill Horace. Once you have made it to the Church of Yorshka Bonfire in Irithyll, Exhaust Anri’s dialogue here. Go ahead and kill Pontiff Sulyvahn, without harming Yuria’s Agent in Chameleon, at the Church of Yorshka Bonfire.
After you have slain Pontiff Sulyvahn, go to Yuria and opt the “Talk” option… She has orchestrated a surprise for you. You and Anri become one. In turn, You bear the Sigils that Anri wore. Head through Irithyll, then hit the Illusory Wall “Gwynn Statue” that is just before the Anor Londo lift. Then speak with Yuria’s Agent down the stairs, and acquire the Sword of Avowal. After acquiring the sword, Proceed down the hall to Anri, and perform… The Wedding Ceremony. If you want Anri’s sword, save and quit, and it will be on Anri’s corpse. And if you want Chameleon, it will be on the corpse of the Agent. Now, Head back to Firelink Shrine, and speak with Yuria. You are now ready, To Usurp, The Flame. All that stands in your way to usurp the Flame, is the Lord of Cinder.
You can summon Yuria for the boss fight, and, if she lives throughout the fight, you can find the Darkdrift and the Black Set where she would be standing in Firelink Shrine. But, if you summoned her for the boss and beat the boss WITH her dying during the fight, then, she will be standing in Firelink Shrine, and her gear will not be available unless you kill her. All that is left, is to expel the one that stands in your place, and take, THE FIRST FLAME. .
As found on Youtube