This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development of 皛 is uncertain. It visually consists of three 白 (white) components, but its original meaning and formation are not clear.
Three whites stacked together suggest extreme brightness or purity, but since the meaning is uncertain, picture a blank white canvas repeated three times to represent something unknown.
For キョウ, imagine three white canvases forming a giant blank 'kyo' (きょ) sign, like a mysterious empty billboard: kyo -> キョウ.