Leann's kanji is "ei" or "kage." It's fifteen strokes long. Its definition is "light; shadow; silhouette; figure; trace." Words formed using this kanji include "eizoo" (image, shadow), "hitokage" (silhoutte"), and "omokage" (face, traaces, vestiges).
Her symbol makes sense if you consider how throughout the game, unless you use Kou frequently and except for the beginning of the game, Leann is nothing more than a shadowed figure. Even with Kou, she's usually only "seen" through her voice conversations with Kou. She's in the game and makes an impact, but except for Kou, no one else knows about her presence.