earthenware vessel in two parts
甗 centers on a specific ancient earthenware vessel made of two stacked parts, likely a steamer or cooking pot.
甗 combines 瓦 (earthenware) with 鬳, which likely contributes the sound and relates to a cooking vessel. The character describes a two-part pottery steamer.
The right side 瓦 means earthenware, and the left side 鬳 looks like a complex stacked structure. Picture a two-tiered clay pot for steaming food.
For ゲン, imagine a genie emerging from this two-part earthenware vessel: genie -> ゲン, and the pot's lid lifts as the genie appears.