This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development of 晎 is uncertain. It visually combines 日 (sun) and 共, but the original semantic or phonetic role of these components is unclear.
With no clear meaning, picture the sun 日 sharing 共 its light, but the scene remains vague—like a kanji whose meaning has faded.
For コウ, imagine the sun 日 and 共 together creating a warm glow: glow -> コウ, though the meaning is uncertain.