jest
詼 centers on playful, humorous speech: jesting or joking with words.
詼 combines 言 (speech) with 灰, which likely contributes the sound and may suggest light, playful talk. The exact historical development is uncertain.
The left side 言 is speech, and the right side 灰 looks like ashes. Picture words as light as ash, tossed around in jest.
For カイ, imagine a jester telling a joke that makes everyone shout 'Kai!' in laughter: Kai -> カイ.