Rui, the Lower Rank Five of the Twelve Kizuki, may have looked like a child, but his story is anything but simple. Once a frail boy desperate to live, he was turned into a demon by Muzan and became obsessed with creating a "perfect family"—no matter the cost. His twisted view of love, power, and control made him one of Demon Slayer’s most chilling and heartbreaking villains.