wipe
揩 centers on the action of wiping something clean or dry, typically with a hand or cloth.
揩 combines 扌 (hand) with 皆, which likely contributes the sound and may suggest the idea of bringing everything together evenly, as in wiping a surface clean.
The hand radical 扌 beside 皆 (all, everyone) suggests a hand wiping a surface until all dirt is gone.
For カイ, imagine wiping a surface with a cloth while saying 'kai' as a sound effect for the wiping motion: kai -> カイ.