shine
焜 centers on giving off light: to shine or glow brightly.
焜 combines 火 (fire) with 昆, which likely contributes the sound and may suggest brightness or a group of flames.
Fire 火 beside 昆 (which looks like a sun 日 over a pair 比) suggests a bright, shining blaze.
For コン, imagine a conflagration (a large, destructive fire) shining brightly: con -> コン.