modest, supple
婧 centers on a graceful, restrained quality in a person: modest in demeanor and supple or pliant in movement. The two given meanings describe a soft, unassuming elegance.
婧 combines 女 (woman) with 青, which likely contributes the sound and may suggest a fresh, youthful quality. The exact historical development is uncertain.
A woman 女 beside 青, which can suggest youth or freshness. Picture a young woman with a modest, graceful posture, moving with supple ease.
For セイ, imagine a modest woman saying 'say' softly: say -> セイ, and her supple voice matches the kanji's gentle meaning.