fluttering of flag, romantic
旎 centers on the soft, flowing motion of a flag or banner, often with a romantic or graceful connotation. The romantic sense is an extension of this elegant, fluttering imagery.
旎 combines 㫃 (flag) on the right with 尼 on the left, which likely contributes the sound. The character originally depicted a flag fluttering gracefully.
The right side looks like a flagpole with a waving banner (方 and the strokes above), while the left side 尼 suggests a graceful, almost romantic motion. Picture a silk flag fluttering romantically in the breeze.
For ジ, imagine a gentle breeze making the flag flutter with a soft 'ji' sound, like the 'gee' in 'gee whiz'—the flag's romantic motion is so surprising: gee -> ジ.