Ayakashi are naturally further in the 'blind spots' than we are. Even if they're big and strong, humans still can't see them.
Recorded? No idea. [He knows one personally, but Hiyori has nothing to do with this. So he'll leave her unmentioned.]

No, and no, probably didn't.

[That question makes him pause for a moment. If only Yukine was at a further canon point... alas.]
I'm not sure? I mean, people are unhappy or mad with god sometimes, when things don't go their way? But I don't know about a grudge.

It sucks waiting for them to practically give us a hint, but I guess we're stuck.
Not really, but keep a sharp eye out for that mask.