Following a year of training, Sakonji Urokodaki stops teaching Tanjiro and leaves him with one final trial. Sakonji will only permit Tanjiro to participate in Final Selection after he successfully slices a large boulder using his sword.
Even after sixth months, Tanjiro is unable to split the stone. Disgruntled, Tanjiro calls out in agony. A mysterious masked boy who is later revealed to be Sabito, appears and managed to escape Tanjiro's sense of smell. He tells Tanjiro a man shouldn't whine before jumping at him. Tanjiro blocks a slash from Sabito's wooden sword, but he's unprepared for a swift follow-up kick.
Sabito states that Tanjiro is slow, weak and immature. He believes that none of these traits are becoming of a man. Tanjiro frantically asks why he was attacked, but the boy in the fox mask simply replies by asking why his opponent is still on the ground.
Tanjiro gets up and Sabito asks him to come at him, but the former is concerned because Sabito is wielding a wooden sword. Amused, Sabito laughs at Tanjiro's gesture. He mocks Tanjiro for worrying his opponent could get injured.
In a flash, Sabito rushes Tanjiro and puts immediate pressure on his defense with a firm strike. He claims to be more powerful than Tanjiro because he's sliced that boulder before. Sabito flips back onto the side of a tree and jumps at Tanjiro from behind. The latter barely parries the strike in time and struggles to follow his opponent as he jumps from tree to tree.
Before long, Sabito knocks Tanjiro to the ground. He scolds him for only memorizing the regiment rather than mastering the Water Breathing forms. Tanjiro is surprised to learn Sabito knows about Sakonji and the breathing technique. Tanjiro's muscle memory doesn't know what it needs to do and Sabito believes he must slam it into his flesh.
The masked swordsman attacks with a flurry of rapid strikes, each representing how much harder Tanjiro must work to pound Sakonji's lessons into himself. The weary defender claims he's been trying hard every day to learn, but he can't make any headway. Sabito says a man must go further beyond and move forward no matter what. He demands to see what Tanjiro is capable of and easily dodges his next attack.
Sabito knocks out Tanjiro with a swift and powerful uppercut from his wooded blade.
A masked girl appears behind Sabito, and he asks her to complete the rest of Tanjiro's training. Tanjiro eventually awakens and tells the girl he wants to be able to fight like Sabito one day. She tells him one day he'll be able to now that he's under her guidance.