This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development is uncertain. The modern form combines 艹 (grass) with 區, but the original semantic and phonetic roles are unclear.
With no clear meaning, picture a rare plant hidden under grass 艹 and inside a container 區, its purpose unknown.
For キュウ, imagine a curious person saying 'Q' (kyuu) when they see this mysterious plant: Q -> キュウ.