かい ends a casual question addressed directly to someone. It often sounds familiar or gentle, though it can also suggest old-fashioned or deliberately characterful speech.
A question for the listener
かい normally asks the listener for an answer rather than expressing private uncertainty. It works especially naturally in simple yes-or-no questions between people with a familiar relationship.
Words and setting can make the ending sound like older or literary dialogue, but the question itself is still addressed directly to the listener.
Casual style versus a neutral question
か is the general question marker and works naturally with polite forms. By contrast, かい belongs to casual, directly addressed speech and adds a noticeable social or character style.
