Smells, like most things, come in boxes.

There are broad scents, bright, loud, that stick to the skin like cloth or sweat. "Human." "Demon." "Cat." "Dead." But there are finer smells, too, smaller boxes you can only identify once you get to know them. More than just a combinaison of demon, human, family, coal, this one is Nezuko;  more than just a mix of human, boar, forest, iron, this one is Inosuke. Even stripped of their outer boxes, even scrubbed clean until the skin is so raw you can almost feel the blood about to leak, people each have their own finer scents that cannot belong to anyone else.

And, here's a funny thing- about smells, about people. The finer you get, The harder it is to pay attention to the bigger boxes. Nezuko is "Nezuko" first- "family," second. "Demon," third. Ironically, the more used you are to a scent, the less you know of it.

So, really, is it so surprising? You shouldn't blame yourself, Tanjiro.

There is no way you could have noticed that your own scent did not contain "human".