flesh, core, pulp, pith
瓤 centers on the soft, inner part of a fruit or vegetable: the flesh, pulp, or pith that surrounds the core. It can also refer to the core itself as the central part of something.
瓤 combines 襄 (likely a phonetic component) with 瓜 (melon/gourd), suggesting the fleshy interior of a gourd or fruit. The exact historical development is uncertain.
The left side 襄 looks like a container, and the right side 瓜 is a melon. Imagine cutting open a melon to reveal its soft, juicy flesh and pulp inside.
For ショウ, picture the soft flesh of a melon being shown to someone: show -> ショウ, as you display the inner pulp.