Lady of Tomes

This might appeal to someone who has come to believe the Greater Will is the real evil and source of all suffering, or some edgelord who wants to make everything miserable, but both of those have better ending options to pursue for their beliefs (Ranni and Dung Eater respectively). The Flame appeals to a different group than either of those though.

The Frenzied Flame instead is presented as both the end of all pain, grief, and woe, but also it represents the option of revenge. You find the Three Fingers at the bottom of a mass grave, full of the victims of a genocide.

In that moment, looking upon the merchant's corpses, it is difficult to imagine anything other than anger and pain. Even if you topple the Golden Order in a different ending, the perpetrators of the atrocity go unpunished. With the flame though, you can exact this vengeance upon the Order. The rest of the world is collateral, but don't they deserve to be punished? Is it really alright to let the world keep going if this is what happens, over and over again?

In reality, odds are the people involved with the genocide of the Merchant Caravans are long gone. They are either dead or functionally so, making any vengeance taken even emptier than it would be otherwise. The Golden Order is corrupt and needs to be dismantled, but to do so at the cost of everyone and everything's life is an insane option. But the Frenzied Flame isn't meant to be rooted in logic, it is instead rooted in gut emotion. That crying sense of injustice, of hatred finally boiling over.

Perhaps that is what makes it the most selfish ending. That embrace of the nihilistic ideal of life being the root of all suffering, life itself being a mistake, and choosing to rectify that is the most self serving possible option. We know this, but it doesn't feel that way in the moment. By making you stand in that mass grave, listening to a half dead man continue playing his song of sorrow, it makes us want to take the flame and burn all that divides and distinguishes.