handle
柲 centers on a handle, specifically the grip of a tool or weapon. It refers to the part held in the hand.
柲 combines 木 (tree/wood) with 必, which likely contributes the sound. The character originally referred to a wooden handle or grip.
The left side 木 suggests wood, and the right side 必 looks like a hand gripping something. Picture a wooden handle being held firmly.
For ヒ, imagine gripping the handle and giving a quick 'heave' to lift the tool: heave -> ヒ.