Webthe question of tanjiro becoming a demon king possibly arises from an event later in the series where, without divulging any major spoilers, tanjiro does.
Webtanjiro's transformation into the demon king showcases the internal battle of good versus evil & redemption.
The change affects tanjiro's relationships with loved.
Webwhether tanjiro is able to become a human again seems dependent on the result of one final struggle within his subconscious.
With muzan having transferred his emotions into tanjiro, he intends to turn him into the new king of demons, claiming that,.