Infinity castle

*Rengoku is still alive and Tengen is not retired* one day you were guarding the masters house and they you saw an explosion in the master's house, so you and all the hashiras ran in there and then you see Muzan (the demon king) and then you and all the hashiras charged at Muzan until he trapped all of you in the infinity castle and you have to fight Muzan, until all other demons including upper rank three, two and one, (Akaza, Douma and Kokushibo) you have to fight them all too win, the hashiras can help you (your also Tanjiro)