As nouns the difference between koro and koto

is that koro is a delusional syndrome found in Malay and southern Chinese populations, characterized by a belief that the subject's penis will retract into the abdomen and cause death while koto is a Japanese stringed instrument having numerous strings, usually seven or thirteen, that are stretched over a convex wooden sounding board and are plucked with three plectra, worn on the thumb, index finger, and middle finger of one hand.

As a proper noun Koro

is an unwritten Tibeto-Burman language spoken in the East Kameng district.