Sakonji Urokodaki informs a curious Tanjiro Kamado about the Demon Slayer Corps, an organization composed of skilled swordsmen trained to kill Demons, despite not being acknowledged or officially recognized by the government.
He goes on to tell Tanjiro about some general information regarding Demons, such as that they must eat humans in order to survive and have special abilities, such as being able to regenerate when they're physically injured. The only way they can be destroyed is through exposure to sunlight or by decapitation with a specialized blade. Despite not knowing much about the origin of Demons, the organization of Demon Slayers have continued to hunt them with their mortal bodies across a number of generations.
Sakonji then introduces his role as one of the many 'cultivators', individuals who train and furnish swordsmen with a variety of techniques and skills. He instructs Tanjiro that if anyone desires to join the ranks of the Demon Slayers, they must first survive an event known as the Final Selection, held at Fujikasane Mountain. Sakonji tells Tanjiro that he will be the one to decide if Tanjiro is qualified to participate in the Final Selection.
After receiving this information from Sakonji, Tanjiro vigorously trains by descending the mountain daily while simultaneously avoiding traps. Through this, he increases his stamina and becomes capable of detecting scents much quicker. Soon after, Sakonji teaches Tanjiro the way of the sword, recovery positions after getting thrown, and breathing techniques.
Meanwhile, Nezuko has fallen into a deep sleep while Tanjiro trains for half a year. Sakonji calls a doctor who comes by to look at her, but he finds nothing wrong with the Demon. Worried that she will die soon, Tanjiro steels himself and trains harder.
After a year of training, Sakonji tells Tanjiro that he has nothing else to teach the boy. Taken aback, Tanjiro notes the time that has passed since their arrival. Sakonji tells the boy to continue improving his techniques and challenges the boy to split a huge boulder in half in order to prove his worth and participate in the Final Selection test. Tanjiro starts to panic, as the task at hand seems impossible with a mere blade. From that day onwards, Sakonji ceases to teach Tanjiro new skills.
As another half year passes, Tanjiro is still unable to split the rock no matter how hard he practices. Feeling extremely disheartened, he yells in frustration, to which a voice asks him to silence himself. Surprised, Tanjiro observes that the voice came from a person wearing a fox mask who was perched on top of the boulder, a person who did not have a scent nor a presence. The masked boy tells Tanjiro to shut up like a man and attacks him with a wooden blade, which Tanjiro clumsily blocks. The boy notes the extent of Tanjiro's weaknesses, deeming him unsuitable to be a Demon Slayer.