strange
瑰 centers on something out of the ordinary: strange, rare, or wondrous. The single given meaning 'strange' captures this idea of being unusual or extraordinary.
瑰 combines 王 (jade) with 鬼, which likely contributes the sound. The jade component suggests something precious or rare, fitting the meaning 'strange' in the sense of extraordinary.
The left side 王 (jade) is a rare and precious stone, and the right side 鬼 (demon) is strange and otherworldly. Together they create the idea of something strange and extraordinary, like a rare jade with an eerie glow.
For カイ, imagine a strange, glowing jade that looks like a kite: kite -> カイ, and the strange jade flies through the night sky.