once upon time, period of time
曏 centers on a past period of time: a moment or era that has already passed, often used in the sense of 'once upon a time' or 'formerly'.
曏 combines 日 (sun/day) with 鄉, which likely contributes the sound. The character is associated with past time, but the exact historical development is uncertain.
The sun 日 over 鄉 suggests a village scene from long ago: picture an old photograph of a rural village under the sun, capturing a moment from once upon a time.
For キョウ, imagine a story beginning 'Once upon a time in Kyoto': Kyoto -> キョウ, and the old capital sets the scene for a past era.