large fishing net
罛 centers on a large fishing net, specifically a wide-meshed net used for catching fish.
罛 combines 罒 (net) with 瓜 (melon/gourd), likely suggesting a net with large, gourd-like meshes. The exact historical development is uncertain.
The top 罒 is a net, and the bottom 瓜 looks like a gourd. Imagine a net with holes as big as gourds, used to catch only the largest fish.
For コ, picture a large net catching a huge fish that makes a loud 'ko' sound as it splashes: ko -> コ.