opening, radiant
奛 centers on brightness and openness: something radiant that opens up or becomes clear. The given meanings 'opening' and 'radiant' both point to a state of expanding light or clarity.
奛 is a rare character. It visually combines 大 (big) and 明 (bright), suggesting a large brightness or opening, but its exact historical development is uncertain.
Big 大 brightness 明: imagine a huge opening letting in radiant light. The top 大 expands the bottom 明 into a wide, open brilliance.
For コウ, picture a radiant opening like a huge 光 (こう, light) shining through: 光 -> コウ, and the big brightness fills the space.