stretch
乀 centers on a stretching or bending motion, like a line that curves or extends. Its standalone meaning is narrow and rare.
乀 is a rare character whose exact historical origin is uncertain. It likely represents a pictographic depiction of a bending or stretching motion.
The single stroke curves downward and to the right, like a line being stretched or bent. Picture pulling a rubber band into a curved shape.
For フツ, imagine the sound of a rubber band stretching and snapping: 'futs!' The sudden stretch sound cues フツ.