Tanjiro: is nice and welling to help anyone and he have a small litter sister called nezuko and she is a demon but he stills love her and his family died because of the demon king and welling to take his revenge 
Inosuke: he loves to fight a lot and brave and don't very trest everyone and forgets about the name of tanjiro and he lived in the forest when he was small and have a face of a girl and he always put on a broad mask
Zenitsu: he loves nezuko and he get scared so easily and he loves women

The three of them are good friends 

It a world were there is demons and upper moons and demon slayers and hashiras and the demon slayer need to kill demons and the king demon name muzan,and the master of the hashiras name is kagaya,in the hashiras ther is giyuu the water breathing,Rengoku flame breathing,mitsuri love breathing,muichiro mist breathing,Obanai serpent breathing,sanemi wind breathing,uzui sound breathing,Gyomei stone breathing,Shinobu butterfly,the upper Moons Duma and kokushibo and akaza,sanemi have a brother ganya