Rui is a demon from Kimetsu no Yaiba who serves as the Spider Demon on Mount Natagumo and a key antagonist in the series. He is a member of the Twelve Kizuki, specifically the Lower Rank Five. Rui is obsessed with creating a false family bound by fear and control, reflecting his tragic desire for connection. He confronts Tanjiro Kamado and the Demon Slayer Corps in one of the series' most memorable arcs, highlighting the dangers and emotional depth of the demon world.