surname, look of a flowing gown
裵 centers on the visual image of a long, flowing gown, often associated with a surname. The surname usage likely derives from the elegant, draping appearance of such clothing.
裵 combines 衣 (clothing) with 非, which likely contributes a phonetic element. The character is associated with the appearance of a flowing gown, and its use as a surname may stem from this imagery. The exact historical development is uncertain.
Picture a long gown (衣) with a distinctive non-straight, flowing pattern (非) that drapes elegantly. The character 裵 captures that flowing gown look.
For ハイ, imagine a flowing gown swaying as you say 'hi' to someone: 'hi' -> ハイ, and the gown flows with the greeting.