How Long Does It Take to Watch 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!