Centuries over centuries of sly, bored contempt for all living things, and sky and stars staying the same. Nothing is ever new - straight up until Hiromasa is.
Seimei clutches to his amusement at first, likening himself to a cat with a new toy, something to be played with and discarded at a whim. Hiromasa is refreshing in his naivety and courageous cowardice, easy to laugh at, sweet, nothing more. Seimei tells himself that until the day he watches Hiromasa give his hand unflinchingly to Lady Sukihime's demon fangs, use his music to guide her gently into human's form; and after that, the lie doesn't much hold. Kindness turns out to be a drug he can't get enough of.
Seimei tells himself, as a last bastion of resistance, that he's perfectly comfortable with watching the mortal world burn around him, crumble into dust, that by involving himself he's only indulging Hiromasa's whims, playing at benevolence. But the truth is - and in the end, alone with himself, Seimei will always come to truth and truth alone - every word Hiromasa says, and every flutter of his awkward hands, and every note floating out of his flute is another stitch pinning Seimei to the fabric of the mortal world and holding him fast.
Seimei finds that he doesn't mind. Centuries of loneliness still stretch ahead, and the sky and the stars stay unchanged, but for now? Everything is new.