parapet, invisible
丏 is a rare kanji whose core idea is something hidden or obscured from view, like a parapet that conceals what is behind it. Its meanings center on invisibility and a low protective wall.
The historical origin of 丏 is uncertain. It may have originally depicted a covered or hidden object, but the exact development is unclear.
The shape looks like a low wall with a curved top, hiding whatever is behind it. Imagine a parapet that makes soldiers invisible to the enemy.
For ベン, picture a bent parapet that hides soldiers from view: bent -> ベン, and the curved wall keeps them invisible.