Fantasy In the Footsteps of Lords (Dark Souls/Elden Ring style boss quest)

You are the Lord of Obsidian Blades. The High Pass Keep has never fallen, and so long as you live, it never will. You have defended it from everything from human bandits through to the Eldest Enemies of All. These days, you mostly are left alone with your musings, but, for some reason, an Unvanquished keeps trying to defeat you.