blind person
瞽 centers on blindness, specifically a blind person. The meaning is narrow and concrete, referring to the condition of lacking sight.
瞽 combines 鼓 (drum) and 目 (eye). The historical origin is uncertain, but it may relate to blind musicians who played drums in ancient times.
A drum 鼓 over an eye 目: imagine a blind person whose eyes are covered by the sound of a drum, relying on hearing instead of sight.
For コ, picture a blind person tapping a drum to call out 'co' as a simple sound: co -> コ, linking the drum component to the reading.