counter for flags
旒 centers on a specific counter used for flags, indicating a tally or enumeration of banners or pennants.
旒 combines 方 (flag) with a phonetic component that also suggests flowing or hanging, referring to the streamers or tassels on a flag, which later extended to counting flags.
The left side 方 is a flag, and the right side looks like flowing streamers. Imagine counting flags by their hanging tassels: each flag has one set of streamers, so 旒 is a counter for flags.
For リュウ, picture a line of flags with long flowing streamers: the word 'long' sounds like リュウ (ryuu) and helps remember the reading.