to rest
呬 centers on resting or pausing, with a nuance of breathing out or sighing in relaxation.
呬 combines 口 (mouth) with 四, which may have originally depicted breath or exhalation. The exact historical development is uncertain, but the character is associated with resting through controlled breathing.
A mouth 口 beside the number four 四: imagine taking four deep breaths to rest and recover.
For キ, picture resting under a key tree: key -> キ, and you pause to catch your breath.