hare's foot fern
荵 refers specifically to a hare's foot fern, a type of fern plant. Its meaning is narrow and botanical, without broader abstract extensions.
荵 combines the grass radical 艹 with 忍, which likely provides the sound. The character was created to name a specific fern, but the exact historical development is uncertain.
The grass radical 艹 sits above 忍, like a fern enduring in the shade. Picture a hare's foot fern growing quietly under a tree.
For ニン, imagine a ninja hiding behind a hare's foot fern: ninja -> ニン, and the fern conceals the ninja.