black ram
羖 centers on a specific kind of sheep: a black ram. The meaning is narrow and concrete, with no clear extended senses.
羖 combines 羊 (sheep) with 殳, which may have originally contributed a sound or indicated a type of sheep. The exact historical development is uncertain.
The left side is a sheep 羊, and the right side 殳 looks like a weapon. Imagine a sturdy black ram with horns as strong as a weapon.
For コ, picture a black ram named Ko: Ko the ram -> コ, and his dark wool makes him stand out.