to make a top knot
鬠 centers on gathering hair into a top knot, a specific hairstyle action.
鬠 combines 髟 (hair) with 會, which likely contributes the sound and the idea of gathering or meeting, reflecting the action of binding hair together into a knot.
The top 髟 shows long hair, and the bottom 會 suggests gathering or meeting. Picture gathering all the long hair together and tying it into a neat top knot.
For カツ, imagine a cat (kat) sitting patiently while you tie its fur into a tiny top knot: kat -> カツ, and the cat's hair is gathered up.