From Webtoon:
Lee Sori is a unique young girl: kind, caring and principled well beyond her years. Unfortunately, these qualities also make her a prime target for bullying. She transfers schools, and just when it looks like history is about to repeat itself, stumbles across a mysterious trail of letters that takes her on a magical scavenger hunt through a hidden world that exists just beneath the surface of her new middle school. A scavenger hunt that will lead her to rediscover friendship, the wonders of nature, and the goodness that still exists within humanity.

Original Webtoon:
Naver Webtoon, Naver Series

Official Translations:
English (Digital, Print), Japanese, Thai, German, Indonesian, Spanish, S.Chinese, T.Chinese

Extra Mini Game (Secret Letter)