mountain in Henan
崤 is a specific place name: a mountain in Henan. It has no broader conceptual center beyond that geographic reference.
崤 combines 山 (mountain) with 肴, which likely contributes the sound. The character was created to name a specific mountain.
The left side is 山 (mountain), and the right side 肴 looks like a mix of meat and a container. Picture a mountain in Henan shaped like a dish of food.
For コ, imagine a small child pointing at the mountain and saying 'co!' as their first word: co -> コ.
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