come together, congregate, meet, cover
盍 centers on bringing things together: people congregating or meeting, and by extension, covering as a result of gathering over something.
盍 combines 去 (go away) and 皿 (dish). The historical development is uncertain, but it may have originally depicted a cover over a vessel, later extended to the idea of gathering or meeting.
Picture a dish (皿) with a lid going away (去) from it, revealing that people have gathered around it. The lid covers the dish when they come together.
For コウ, imagine a group of people coming together under a large coat (コート) that covers them all: coat -> コウ.