This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
妎 combines 女 (woman) with 介, but the historical origin and original meaning are uncertain. It may have been a phono-semantic compound, but the exact development is unclear.
With no clear meaning, picture a woman 女 standing beside a boundary 介, perhaps feeling envious or troubled—hinting at the vague negative nuances sometimes associated with this rare character.
For カイ, imagine the woman 女 calling out 'Kai!' across the boundary 介, as if trying to get attention: Kai -> カイ.