ribbon or cord used attach ornaments
紱 centers on a ribbon or cord used to attach ornaments, likely a decorative or functional tie.
紱 combines 糸 (thread) with 犮, which likely contributes a phonetic element. The exact historical development is uncertain, but the thread component clearly relates to the ribbon or cord meaning.
The left side is thread 糸, and the right side looks like a person pulling something. Imagine a thread being pulled into a ribbon to attach an ornament.
For フツ, picture a ribbon so tight it makes a 'foots' sound when plucked: foots -> フツ, and the ribbon holds the ornament in place.