That’s very hard to say, Muzan inject his blood in Tanjiro’ body, but does not seems to be possess
The way I see it Muzan is dead - 100%. All he did was plant in Tanjiro was his memories and cells from his body. so I don't think he is technically controlling him. I see it as Tanjiro being his own demon but with memories,etc of Muzan. Thus Muzan "can live" through him. At least that's my way of seeing it. But you never know a future chapter can twist this thought of mine. lol
Lol indeed that’s what I thought
So from what we read, is Tanjiro being control or is he just a new demon?