The battle against Akaza was long and well-fought, but it ended with Tanjiro using his own blade as a projectile weapon. Why did Tanjiro throw his sword at Akaza?
Tanjiro decides to throw his sword at Akaza because the demon is running away. The sun is rising, which forces Akaza to retreat into the nearby woods. Tanjiro is injured and can’t make chase on foot, so he throws his sword through the fleeing Akaza’s back.
The sword ends up lost and Tanjiro must receive a new one from his swordsmith.
Tanjiro decides to throw his sword at Akaza
In chapter #65, Rengoku’s battle against Akaza winds down. Rengoku didn’t become a demon, turning down Akaza’s offer. Despite the demon’s arm penetrating his chest, Rengoku is able to hold Akaza in place in an effort to remove his head. The sun is also rising, which allows for another opportunity to end Akaza.
Noticing the rare opportunity, Tanjiro grabs his sword and calls out for Inosuke to go in for an attack. Inosuke is able to approach with his Beast Breathing: First Fang, but Akaza tears off his own arms in an effort to escape Rengoku’s grip.
The demon realizes the sun is rising. In an effort to save himself from turning to dust, Akaza sprints into the nearby shaded woods. It is impossible for Tanjiro to catch up with his injuries.
Reeling his weapon back, Tanjiro is able to throw his sword at the fleeing Akaza. The blade blasts through the trees and foliage, striking Akaza through the back.
“Where are you going, you coward,” Tanjiro screams. “Don’t run away!”
Tanjiro’s words offend Akaza. The demon thinks to himself that he’s not running from the Demon Slayer, but rather from the sun.
Akaza’s cowardice angers Tanjiro, who exclaims that humans are made of flesh and blood that don’t grow back. The Demon Slayers are always fighting on the demons’ advantage during the nighttime.
“You’re afraid to admit that you haven’t won today,” Tanjiro says. “Rengoku hasn’t lost… He didn’t let anyone die!”
So that’s the answer. Tanjiro decides to throw his sword at Akaza because the demon is fleeing. Tanjiro is too injured to pursue on foot, so he turns his blade into a projectile.