The boy with a fox mask challenges Tanjiro to a fight to which he declines, as the stranger is only wielding a wooden sword while Tanjiro has with him a real sword. The boy laughs at Tanjiro's ignorance and declares that as someone who had succeeded in splitting the boulder, he wouldn't be hurt by someone weaker. He proves this by easily defeating Tanjiro, telling him that he does not yet fully understand Sakonji's breathing techniques to be able to utilize them properly. Tanjiro is taken aback at the fact that this stranger mentioned Sakonji. After another brief match, the stranger knocks Tanjiro out cold. As the masked stranger walks away, a girl with a floral patterned kimono approaches, and the boy tells her to take care of the rest.
When Tanjiro awakens, he sees the girl and asks her if she had witnessed the fight. He also tells her he wants to be as skilled as the boy someday. The girl replies that he will indeed be able to master those techniques one day, and she will be there to witness his strength. Tanjiro requests for her name, thinking to himself that the girl is cute. She introduces herself as Makomo and the boy with the fox mask as Sabito.
Over time, Makomo acts as Tanjiro's teacher to aid him in correcting his sword postures and breathing techniques. When Tanjiro asks why she was willing to teach him, she only replies, "we all really like Urokodaki-san," as her catch phrase. Makomo also informs Tanjiro that Sabito and her are not siblings, rather orphans taken in by Sakonji along with many children that are currently watching him. She continues to guide him as he keeps battling against Sabito, though the latter always manages to defeat him.
Half a year of training passes, and Sabito finally comes to challenge Tanjiro with a real sword with Makomo as a bystander. A determined and changed Tanjiro tells Sabito that he will win, striking at his opponent before he could react. Tanjiro's blade cuts Sabito's mask in half to reveal a gentle, smiling boy with a scar on his right cheek. Makomo, keeping her promise to witness Tanjiro's progress, tells Tanjiro to win and triumph against "that person," fades away as mist clouds her and Sabito.
When Tanjiro comes back to his senses, Sabito is gone but the boulder in front of him is split in half, just like Sabito's mask.