This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
嵑 combines 山 (mountain) with 曷, which likely contributes a phonetic element. The exact historical development is uncertain.
The left side is a mountain 山, and the right side 曷 looks like a person under a roof with a sun-like shape. Without a clear meaning, picture a mysterious mountain with a hidden structure on top.
For ケツ, imagine a mountain so tall it makes you say "kets!" as you climb it: kets -> ケツ.