How to Find Fia and Complete Her Quest

First Meeting - Roundtable Hold: Find Fia in a side room. Accept her embrace to receive a Baldachin's Blessing. You can return for more after using one.

Second Meeting - Roundtable Hold: After Rogier returns and you exhaust his dialogue, speak to Fia again. Ask her something to receive information about Rogier and a note with the location of the Black Knifeprint. Obtain the Black Knifeprint by following Rogier's questline and return it to Fia.

Third Meeting - Roundtable Hold: Trigger this step by obtaining at least two Great Runes and reaching the Altus Plateau via the Grand Lift of Dectus. Speak to Fia and accept her embrace. She will give you the Weathered Dagger. Give this dagger to D. Rest at a Site of Grace to refresh Roundtable Hold. The door near Smithing Master Hewg will now be open. Enter to find D dead and Fia standing over him. Collect D's Bell Bearing and the Twinned Set from his body. Do not alter the Twinned Set.

Fourth Meeting - Deeproot Depths: Travel to Deeproot Depths by going through Siofra River and defeating the Valiant Gargoyle & Valiant Gargoyle (Twinblade) boss. Use the coffin beyond the Aqueduct-Facing Cliffs Site of Grace. Progress through Deeproot Depths to the Across the Roots Site of Grace. Head into the open area to fight Fia's Champions. After the fight, speak to Fia and agree to let her hold you. She will reveal she is looking for the Cursemark of Death.

Obtain Cursemark of Death: Progress Ranni's Questline until you obtain the Cursemark of Death. If you already have it, you can proceed.

Fifth Meeting - Deeproot Depths: Hand over the Cursemark of Death to Fia. Exhaust her dialogue and rest at a Site of Grace. Speak to her again to enter Godwyn's dream and fight Lichdragon Fortissax.

Quest End - Roundtable Hold: After defeating Lichdragon Fortissax, you will obtain the Mending Rune of the Death-Prince. If you advanced D's Twin Brother's Quest by giving him the Twinned Set, reload the area to obtain Fia's Armor Set. Reload again to find D's Twin Brother over Fia. Reload once more to find the Twinned Set and the Inseparable Sword as final rewards.