He is like the moon, his other like the sun. The purpose they follow is endless, therefor they must be as well.
He but the reflection of his other, the moon to the sun.
The markings on their faces grow and fade as they switch places.
The sword is the bridge between them, like the earth between the sun and moon.
They, and their world, have a sort of terrifying beauty. I want to touch it, and them, but I am afraid that I'll burn, or be poisoned, or dissolve all together. Alluring, dangerous.
He loves to confuse, and perhaps scare, others. It is, I think, his hobby as he hunts his prey, something to amuse himself.
Perhaps, some say, he to is a mononoke. I do not know if that is true, or even completely valid. But it is an interesting notion.