juice
糔 centers on the liquid extracted from something, specifically juice. It is a rare character with a narrow meaning.
糔 combines 米 (rice) with 蚤, which likely contributes the sound. The exact historical development is uncertain, but it probably relates to extracting liquid from grain.
The left side is 米 (rice), and the right side 蚤 looks like a flea. Imagine squeezing a flea out of rice to get a tiny drop of juice.
For シュウ, imagine a shoe filled with rice juice: shoe -> シュウ, and you have to squeeze the juice out.