Nakime is arguably one of the most terrifying demons not because of her combat power, but because of her utility. As long as she is alive and playing her biwa, the is inescapable. She can teleport a Hashira into a pit of demons or move a dying Upper Moon away from a decapitation. Her silent, floating presence in the shadows makes the castle a "living" organism.
A hand grabbed his haori. It was Nezuko—still in her bamboo muzzle, her eyes wide but calm. She pointed. Through a sliding door, Tanjiro saw a distant figure: a pale young man with rainbow-patterned eyes and a mocking smile, playing a biwa. Nakime, the new keeper of the Castle, plucked a string—and the entire floor beneath them tilted, spilling them into different levels of the infinite labyrinth.
'Demon Slayer: Infinity Castle' Review: Haruo Sotozaki's Visually
The Infinity Castle Arc is widely regarded as the shonen series' emotional and strategic peak.