"Kai" is already a fairly common and accepted spelling, especially in English-speaking countries.
However, here are some potential variations, mostly based on different languages or cultural contexts:
* Khai: This is a common variation in Vietnamese.
* Cay: This is a variation in some African languages.
* Ki: This is a shorter, more minimalist variation.
* Kye: This is a variation that emphasizes a specific pronunciation.
Ultimately, the best spelling will depend on the specific context and your personal preferences.