This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development of 靎 is uncertain. It visually contains 雨 (rain) on top and 鵭 (a rare character possibly related to a bird) below, but the original semantic or phonetic motivation is unclear.
Since the meaning is uncertain, focus on the shape: rain 雨 falling over a bird-like shape 鵭. Imagine a rare bird that only appears in the rain, but its name and purpose are unknown.
For カク, imagine a rare bird hidden in the rain making a sharp 'kak' sound: kak -> カク. The bird's call is the only clue to its name.