though, notwithstanding, while, during, both, all
乍 centers on a sense of simultaneity or concession: something happening while something else is true, or a contrast like 'though' or 'notwithstanding'. The meanings 'both' and 'all' extend this idea to inclusive simultaneity.
The exact historical origin of 乍 is uncertain. It may have originally depicted a tool or action, but its modern use as a character for 'while' or 'though' is likely a phonetic loan. The character is now primarily known as a component in other kanji.
The shape 乍 looks like a person 人 with an extra stroke, as if caught in the middle of an action. Imagine someone pausing mid-step: while they are moving, they are also still. This captures the idea of 'while' or 'though'.
For サ, picture a person sighing 'Sah...' while pausing mid-action, as if conceding a point: Sah -> サ, and the pause reflects the meaning of 'though' or 'while'.