beauty
姁 centers on feminine beauty, likely describing a woman's graceful or attractive appearance.
姁 combines 女 (woman) with 句, which likely contributes a phonetic element. The exact historical development is uncertain, but the character is associated with the idea of feminine beauty.
A woman (女) beside a curved, graceful shape (句) suggests a beautiful, elegant figure.
For ク, imagine a beautiful woman named Ku, whose name sounds like 'coo'—a soft, admiring sound: Ku -> ク.