scallion, shallot
薤 centers on edible allium plants with layered bulbs and slender leaves: scallions and shallots. The two given meanings are closely related members of the onion family.
薤 combines the plant radical 艹 with a phonetic component historically related to 韮 (leek) and 歹, suggesting a type of allium. The exact historical development is uncertain.
The grass crown 艹 sits above a structure that looks like a leek 韭 growing from the ground 歹. Picture a scallion pushing up through the soil with its green leaves spreading out.
For カイ, imagine a scallion shaped like a kite: kite -> カイ, and the long green leaves trail behind like a kite tail.