Children who Chase Lost Voices

Strange sounds in the darkness... Unearthly music from an old crystal radio... These are all the warning Asuna Watase has before a simple walk to her clubhouse catapults her into a nightmarish adventure that will take her beneath the Earth to a lost land beyond the realm of legend! Attacked by a strange monstrous creature, rescued by a mysterious stranger and pursued by a relentless enemy, Asuna finds herself enmeshed in a centuries old mystery that will bind her to a strange young defender and lead her inevitably, towards a secret that may hold the key to life itself!

(Source: Sentai Filmworks)