I just realized that the Chinese character for Qian, the Heaven Trigram, is 乾, which in Japanese also means "dry."
Which makes the concept of "drying out" in Karakasa make a hell of a lot more sense.
The Ooku is a place where one aspires to Heaven, to the divine, metaphorically via its connection to Tenshi, the "son of Heaven," the highest-ranked position in the land, and more literally via the worship of Omizu-sama. Tenshi saying "I am dry" refers to his supposedly divine status, and being or becoming dry means seeking or maintaining a divine status.
Hence the risk of "drying out" when one enters the Ooku and begins this aspiration.
I think the idea is that it's necessary to maintain balance between being "dry" and being "wet," or between Heaven and earth, and to not lose touch with "earth" in one's quest for the divine.
Movie Medicines Seller, who carries the sword of Kon, Earth, is there to correct the "drying out" of those who have lost their connection to earth in their aspirations to Qian (乾, Heaven) or to kawaki (乾き, dryness).
