ancient ordinary kimono
褂 refers to a type of ancient ordinary kimono, specifically an unlined robe or coat worn in historical contexts.
褂 combines 衤 (clothing) with 卦, which likely contributes the sound. The character is used for a historical garment, but the exact origin of the compound is uncertain.
The clothing radical 衤 beside 卦 suggests a specific garment. Imagine an ancient diviner wearing a simple unlined robe while casting hexagrams: 褂 is that ordinary kimono.
For ケイ, picture a traditional robe worn by a character named Kay: Kay -> ケイ, and she always wears this ancient kimono.