In the premiere episode of " Demon Slayer: Kimetsu no Yaiba ," entitled "Cruelty," Tanjiro Kamado's life is shattered when he discovers his family has been slaughtered by a demon, with his sister Nezuko being the only survivor but transformed into one. While trying to save her, they are confronted by the demon slayer Giyu Tomioka, who spares them after witnessing Nezuko's protective behavior towards her brother, setting them on a journey to find a cure. You can find detailed plot breakdowns of this episode and others through this Kimetsu no Yaiba Wiki article and this Medium review .