It's the best sort of discovery. Would Natsume be disappointed to find out he's not not!human? (They..are only humans in EnStars, right?) Recently sounds good, playing out the weird getting to know each other stuff would be fun. Kiyoshi would have some complicated feelings too but more about that he didn't know about him earlier, than about him existing at all. That's actually not much of a surprise. The only question then is if it's recent as in a week ago recent of a few months ago recent, or however long it might have been.