Pretty much let me give you a explanation, instead of Muzan killing Tanjiro's family (which I'll get back to that) Muzan killed Kaigaku and Zenitsu's sensei, turning Kaigaku into a demon. At this time Zenitsu was busy training trying to get his mind off things. Now time to explain Nezuko and Tanjiro's situation. In this AU Nezuko was heartless and cared only about herself and once she met Akaza and noticing his strength immediately fell to her knees and begged to be spared (Obviously cause Akaza doesn't kill women) He decided to turn her into a demon. In which she came back home and killed her and Tanjiro's family while Tanjiro went out to bring the coal down the mountain. Tanjiro's mother on her final breathes told Tanjiro and now he has a mission to defeat and ask Nezuko why she would do this. Inosuke, well. He's just Inosuke Zenitsu: Talking to Tanjiro Inosuke: poking Kaigaku "Fight me demon!" Kaigaku: annoyed grumbles (Quick note you can be Nezuko, Tanjiro, Giyuu, Zenitsu, Inosuke or Kaigaku*