Tanjiro's journey always hits me a bit sideways. The growth isn't this smooth hero's arc; it's this clumsy, desperate scramble to get strong enough fast enough to save his sister, and that desperation shapes everything. You see him absorbing techniques not because he's a prodigy, but because failure means Nezuko dies. The conflict with demons is brutal, sure, but the deeper tension is this constant race against a clock only he can hear.
Where it gets really interesting for me is how the Hashira, the top-tier slayers, reflect different facets of that growth. Someone like Shinobu, who lacks the physical strength for decapitation, embodies a completely different kind of strength—strategic and poisonous. It suggests there's no one right path to power, which complicates Tanjiro's more straightforward 'master the breathing forms' approach. The internal struggle often felt more pronounced than the flashy fights, like his battle to maintain his kindness in a world that keeps demanding ruthless efficiency. He has to constantly reconcile his compassion with the brutal necessity of his mission.
Zenitsu's a perfect example of growth that isn't linear. He's still a coward in a lot of fights, but his moments of unconscious competence show that the skill is in there, buried under layers of panic. That feels more real than someone just 'getting over' their fears. The manga lets characters be flawed and capable simultaneously, which is where a lot of the emotional payoff comes from—seeing that buried strength flicker to the surface at the exact moment it's needed, even if it goes back into hiding afterward.