net
罟 centers on a woven mesh used to catch things: a net.
罟 combines 罒 (net) with 古, which likely contributes the sound. The character is a phono-semantic compound for a net.
The top 罒 is a net, and the bottom 古 looks like an old frame. Picture an old woven net stretched on a wooden frame.
For コ, imagine a small child (子, こ) playing with a net: 子 -> コ, and the child catches things in the net.