I have always known
That at last I would
Take this road, but yesterday
I did not think that it would be today.
The end comes for all. This is the whole of it, the one immutable truth of the universe. Mountains crumble, rivers run dry in their beds. In the end, there is only ash.
The end, when it comes, is seldom peaceful. Acceptance is no easy thing, as inevitable as it may be. Mortal things ache for permanence, cling to this world for longer than they should, fueled by love and hate and sorrow, the infinite array of delicate, complex human emotion that leaves its stain behind, tiny fragments of souls who do not know how to move on. It has been his job, for a very long time now, to kill them. The world cannot continue in its proper order when things that should be resting quietly in the grave rage through the night, terrifying the living.
His own mortality has never been a subject of much contemplation. He has loved a long, long time now, unchanged, unmolested by the hands of time and the corruption of age. And yet he knows—has known for for nearly as long as he's been ridding the world of that which does not belong—that he is hollow. Without the other who claws at his skin from the inside, he would crumble to dust. That is the way of things.
Still, it comes as a surprise. Sprawled on the cold ground, blood soaking into the frosted and leaves, becoming one with the earth at last, he stares up into that shining bronze visage.
"Ah." His voice is the wind in the trees, a scrape of bare branches. It rattles in his chest and he does feel remarkably hollow at this moment, as if the marrow has been sucked from his very bones. "I see."
His face feels bare now, white like bleached bone, and his body is heavy. His other stares back with inhuman eyes, framed by a canopy ablaze with red and yellow and orange. He can read no emotion there. The mononoke is dead, his other's thirst quenched, and the thin threads of reality seem to be slowly dissolving around them. "I had not realized." The rust of blood has replaced his painted smile, blue eyes gone dull. "It is done, then."
There is no one to hear his words. He laughs, once, voice gone as empty as the rest of him, and accepts oblivion.