Kimetsu no Yaiba Season 1 Episode 8.
The bystander Kibutsuji strikes turns and bites his wife he was walking with, forcing Tanjiro to leave Kibutsuji to subdue him, and Kibutsuji takes advantage of the chance to leave with his “family.” Police arrive and try to pull Tanjiro off the demon, but he won’t move as this will let the demon escape. A nearby demon, Tamayo, uses a Blood Art spell to blind the police, having noticed Tanjiro was still trying to save the demon and wants to help. She confirms she and her companion Yushiro are demons to a shocked Tanjiro, but she is also a doctor who wants to kill Kibutsuji. Kibutsuji meanwhile, sends his family ahead to their home and orders two demons to bring him Tanjiro’s head. Tanjiro retrieves Nezuko and Yushiro leads him to Tamayo’s cloaked house, where she is treating the bitten woman, her husband restrained in the basement. Tamayo tells Tanjiro she can treat the woman without being overcome by hunger because she has tweaked her body and removed Kibutsuji’s curse so she and Yushiro can live without eating humans, needing only a bit of human blood. She also reveals she turned Yushiro into a demon, despite the general belief only Kibutsuji can do so, as she developed the ability after two hundred years. She clarifies she’s not trying to make more demons, and only turns humans who agree to it when it is clear they will otherwise die. Tamayo is also searching for a way to return a demon to a human and asks Tanjiro to let her study Nezuko’s blood, as she is special for being able to sleep long periods of time without eating and for freeing herself from the bloodlust, and to bring more blood from other powerful demons for her to study. Tanjiro agrees to help. The two demons Kibutsuji sent, Susamaru with temari balls, and Yahaba, with eyes with arrows for pupils on his palms, find and attack the house.