sob, choke, crooked heaven radical variant (no.71)
旡 centers on a choked, stifled sound: sobbing or choking. The radical sense is a variant of the 'crooked heaven' shape used as a component in other characters.
旡 is traditionally explained as a pictograph of a person with a blocked throat, representing choking or sobbing. The exact historical development is uncertain.
The shape 旡 looks like a person (the lower part) with something caught in the throat (the upper horizontal stroke), causing them to choke and sob.
For キ, imagine the choked sound 'key' stuck in someone's throat: key -> キ, and they can't get the word out.