You Must Master a Single Thing

While searching for Nezuko, Zenitsu finds captured Demon Slayers transforming into spiders. "Son" of the Spider Family emerges, revealing he has been bitten. Believing he will die, he reminisces on his past and reflects on how he repeatedly refused to train despite wanting to make his master proud. Zenitsu loses consciousness and attacks Son, who continually interrupts his form, the first and only form of Thunder Breathing he can do. Despite being poisoned, he beheads Son with his own variation of Thunder Breathing before attempting to slow the poison. Tanjiro and Inosuke encounter “Daughter” when she calls to her “Father”, who emerges from the forest.