ancestral offering receptacle, coral
瑚 centers on a precious vessel used in ancestral rites, and by extension the coral-like material from which such vessels were sometimes made. The two meanings connect through the idea of a treasured, ornate receptacle.
瑚 combines 王 (jade/jewel) with 胡, which likely contributes the sound. The character originally referred to a ritual vessel made of precious material, later extended to coral.
The left side 王 (jewel) suggests something precious, and the right side 胡 (a phonetic component) can be imagined as an ornate container. Picture a jewel-encrusted ancestral offering vessel made of coral.
For コ, imagine a small, precious coral vessel that is a "co"-llector's item: co -> コ, and the jewel-like coral makes it a treasure.
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coral
tabulate coral (extinct coral of the order Tabulata)
tabulate corals (extinct corals of the order Tabulata)
coral wedding (anniversary); 35th wedding anniversary
sweet viburnum (Viburnum odoratissimum)
Cornus alba
Coral Sea
corallite
coral (color); light red
Brazilian plume flower (Justicia carnea); Brazilian plume
coral snake
organ-pipe coral
brain coral
red coral (Corallium japonicum)
yellow clown goby (Gobiodon okinawae)