Demon Slayer: Kimetsu no Yaiba - S01E04 - "Final Selection"

Two years have passed since Nezuko's transformation, and Tanjiro leaves for the Final Selection. Before his departure, Urokodaki warns him that a demon's strength is equivalent to the number of humans it has eaten, gifting him a fox mask with a protection spell.

Tanjiro reaches Mt. Fujikasane, where wisteria flowers bloom year-round, creating a prison for demons, and is informed that to pass the test, the applicants must survive there for 7 days.