Koyuki is a minor character associated with Kimetsu no Yaiba. She is best known as the young girl connected to Hakuji's past, appearing in the backstory that helps explain his tragic transformation and motivations. Koyuki represents innocence, compassion, and the human bonds that shape key events in the series. Her presence is important mainly as part of the emotional foundation behind one of the story's major antagonists, giving depth to the themes of loss, love, and regret.