callus, corn
胼 centers on hardened skin that forms from repeated pressure or friction: a callus or corn.
胼 combines the flesh radical ⺼ with 并, which likely contributes a phonetic element. The exact historical development is uncertain.
The flesh radical ⺼ on the left suggests skin, and the right side 并 looks like two hardened layers pressed together. Picture skin thickening into a callus where it is repeatedly rubbed.
For ヘン, imagine a hen pecking at a hard corn on your foot: hen -> ヘン, and the callus feels like a tough kernel.