tiger, brave, fierce, surname
乕 centers on the tiger: a fierce, brave animal. The surname sense is a natural extension of the tiger's symbolic strength.
乕 is a variant form of 虎 (tiger). The exact historical development of this simplified shape is uncertain, but it likely derives from a cursive or abbreviated version of the tiger pictograph.
The top 厂 suggests a cliff or shelter, and the lower part 巾 looks like a hanging cloth. Picture a fierce tiger hiding behind a cloth near a cliff, ready to pounce.
For コ, imagine a brave tiger named Ko: Ko the tiger -> コ, fierce and bold.