In the anime series "Demon Slayer: Kimetsu no Yaiba," the haunted house serves as a test for Tanjiro, Inosuke, and Zenitsu during their training in the Entertainment District arc. The haunted house challenges the demon slayers to face their fears and weaknesses, pushing them to overcome their limitations and grow stronger both mentally and physically. It also serves as a way to train their senses and instincts, preparing them for future battles against demons.