This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development is uncertain. The character combines 歲 and 頁, but the original semantic and phonetic roles are unclear.
The left side 歲 suggests age or years, and the right side 頁 is a head or page. Without a clear meaning, picture an ancient head-shaped relic whose purpose is forgotten.
For カイ, imagine a mysterious old head (頁) that whispers 'kai' when you touch it: kai -> カイ.