die
薨 centers on the act of dying, specifically used in historical contexts for the death of a high-ranking person such as a feudal lord or noble.
薨 combines the plant radical ⺾ with 死 (death). The exact historical development is uncertain, but it likely relates to the idea of withering or falling like a plant as a metaphor for death, especially of nobility.
The top part looks like a plant (⺾) and the bottom is 死 (death). Imagine a noble lord's life withering away like a dying plant, marking his passing.
For コウ, picture a noble's death being announced with a deep, resonant gong: the sound 'ko' echoes as the lord passes away.