crotch
胯 centers on the crotch area of the body, where the legs meet the torso.
胯 combines ⺼ (flesh/body part) with 夸, which likely provides the sound. The character specifically denotes the crotch region.
The left side ⺼ indicates a body part, and the right side 夸 looks like a person with legs spread. Together they point to the crotch area between the legs.
For コウ, imagine a coach (コウ) telling you to stretch your crotch area before a game: coach -> コウ, and the stretch targets the 胯.