Fia

At the Roundtable HoldLandmark, ask Fia to hold you and receive a Baldachin's Blessing.

Ask Fia to hold you again, then choose the “talk in secret.” Fia will then give you a special dagger. In our testing, we were able to trigger this both by reaching Altus PlateauGrace and by asking for several hugs before Altus PlateauGrace.

Give the dagger to D in Roundtable HoldLandmark.

Return to the Hold to find Fia over D's body. Speak to her, and she will disappear.

Find Fia in Deeproot DepthsGrace, defeat her guards, and ask to be held again.

Bring her the Cursemark of Death. Exhaust her dialog and reload until you can enter the Deathbed Dream, and defeat Lichdragon Fortissax. Receive mending rune from Fias body.