stepping stone, hard, serious minded
矼 centers on a firm, unyielding quality: something hard like a stepping stone, and by extension a serious, steadfast mindset.
矼 combines 石 (stone) with 工, which likely contributes the sound. The character suggests a stone that is hard and firm, like a stepping stone.
A stone (石) that is worked (工) into a solid stepping stone: hard and reliable, like a serious-minded person.
For コウ, imagine a hard stone step that makes a loud 'koh' sound when you step on it: koh -> コウ, and the stone is firm and serious.