Can't really recall the barrier part, but doesn't she, like, go in-and-out quite often?
As for the recent incident... 🤔 while not mentioned, I think there's a pretty good chance that Kasen was also in on it, or at the very least was aware about the plan. Remember, this was a legitimate, actual crisis. Every sage was definitely at least informed. Besides, how much involved can you be? One of the stones got Okina's power. And Yukari? She's just the one who slipped the stones into Reimu's and Marisa's hands.
Hmm... Misumaru's the one who made the stones, so I guess Kasen could be the one who gathered the appropriate materials?
