This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
痎 combines 疒 (sickness) with 亥, which likely contributes a phonetic element. The exact historical development is uncertain.
The sickness enclosure 疒 wraps around 亥, suggesting an illness. Without a clear meaning, picture a mysterious ailment hidden inside.
For カイ, imagine a person named Kai who falls ill with this mysterious sickness: Kai -> カイ.