dim light, glimmer, warm
熺 centers on a soft, subdued light that also brings warmth: a dim glow or glimmer that feels warm.
熺 combines 火 (fire) with 喜, which likely contributes the sound and the idea of joy or pleasure, suggesting a pleasant, warm glow.
Fire 火 beside joy 喜: imagine a cozy fireplace giving off a dim, warm light that makes you feel happy and content.
For キ, picture a key glowing with a dim, warm light: key -> キ, and the key's soft glow matches the kanji's meaning.