In the Taisho-era Japan of Demon Slayer, where humans battle nocturnal demons, young Mio Hayashi hails from a rural village plagued by demon attacks. Orphaned at a young age after a demon raid, she was rescued and trained by a wandering Slayer. Now a spirited trainee, Mio attends a hidden academy disguised as a school to hone her skills. With her unique heterochromatic eyes—one green, one blue—and freckled tan skin, she wields a small Nichirin blade, determined to protect her new family of Slayers while uncovering the truth behind her parents' fate.