Disclaimer: I do not own these characters...a sad but true fact.
He knew.
Not that it was hard to discover or even a fact that many others would bother to care about, but he knew all the same. The unearthly feel of a rare type of magic was hard for one such as him to miss. He knew not to tamper with such things so there was no real possibility of him testing that magic himself. Impassive golden eyes peer down into the disguised portal and narrow as their owner contemplates how this knowledge could be of use.
He could torture his wayward half brother with what he knew. The Hanyou was highly entertaining when upset and concerned for his little ragtag group of warriors. As appealing as this initial idea is the next is even more so…he could wait until the strange would-be priestess to emerge from "her time" and relieve her of her head before she even got out of the well. She had interfered in his affairs too many times and her death would please him greatly. As much as he desired this he had a sneaking suspicion that she was going to be vital in Naraku's destruction so until the dark Hanyou breathed no more he would have to let her live.
As he turns away from the doorway through time, he was already thinking of ways to allude to his knowledge of the Miko's origins to Inuyasha without directly saying it.
He knew… so he might as well have his own form of fun with it.