Tập 11: Airi điều tra những âm thanh bí ẩn tại Hang Trăm Yoshimi ở Saitama

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After leaving Nikko, Airi hears a mysterious sound only she can hear. They head to the origins of that sound, to find out that it's the Yoshimi Hundred Caves in Saitama, a historical site. (Source: Crunchyroll)