Twisted memories are a

Izuku grew up with a quirk that let him follow someone else chosen by his quirk in the past. Tanjiro grew up knowing that someone or something followed him around half of the time he was awake gradually growing to the point of seeing the boy following him when he took over dancing the yearly kagura. Knowing the two would grow closer with time, Izuku feared something would happen. Following his gut he mentioned nothing of this ominous feeling to Tanjiro. Watch as these two boys grow as siblings and in power to defeat the demons of the past for Tanjiro, along with the demons in the current for Izuku.