Cursemark of Death is a Key Item in Elden Ring.
This item is part of Fia, Deathbed Companion's questline.
Cursemark carved into the discarded flesh of Ranni the Witch.Also known as the half-wheel wound of the centipede.
This cursemark was carved at the moment of Death of the first demigod, and should have taken the shape of a circle.
However, two demigods perished at the same time, breaking the cursemark into two half-wheels.
Ranni was the first of the demigods whose flesh perished, while the Prince of Death perished in soul alone.
Area: on the remains of Ranni the Witch's original body atop of the Tower, alongside the Stargazer Heirloom. This area can only be reached from the Carian Study Hall, after placing the Carian Inverted Statue, received from Ranni in exchange for the Fingerslayer Blade of Nokron, Eternal City, on the altar at the entrance.
Give it to Fia and, after reloading the area, interact with her to enter the Deathbed Dream, where Lichdragon Fortissax can be challenged. After defeating this boss, retrieve the Mending Rune of the Death-Prince from Fia's corpse: you will now be able to attain the Age of the Duskborn ending after defeating the final boss.