round
囘 centers on the idea of roundness or circular motion: something that goes around, returns, or revolves.
囘 is an older variant form of 回, which depicts a revolving or circular motion. The outer enclosure 冂 and inner 巳 together suggest something turning or returning.
The outer 冂 frames an inner 巳, like a coiled shape turning around itself. Picture a snake curling into a round loop inside a box.
For カイ, imagine a round kite (カイト) spinning in circles: kite -> カイ, and the kite's looping flight matches the round, returning motion of 囘.