Akaza and Rengoku have an intense battle with Tanjiro sitting on the sidelines. Why didn’t Tanjiro help Rengoku?
Tanjiro didn’t help Rengoku because he had a severe stomach injury. Rengoku orders Tanjiro not to intervene, saying his wound will open up and become fatal.
Inosuke is able to jump in when Akaza is held in place by Rengoku, but it’s too little too late.
Tanjiro is told not to help Rengoku
Chapter #63 begins with Akaza, the Upper Rank 3 demon, approaching Rengoku and Tanjiro. Previously, the Demon Slayers successfully end The Sleep Demon’s life, with Tanjiro sustaining a stomach injury.
In the blink of an eye, Akaza attacks Tanjiro. Rengoku is able to repel the demon away with Flame Breathing: Second Form.
The Flame Hashira takes note of Akaza’s fast regeneration and overwhelming demon aura. He quickly concludes that Akaza must be an Upper Rank demon.
Rengoku asks why someone so powerful would attack a wounded person first. Akaza replies, saying that Tanjiro might interrupt the conversation that’s about to be held.
Akaza points out that he and Rengoku have very different values. They both say they hate each other despite meeting for the first time.
Rengoku is asked to become a demon
The Upper Rank demon then propositions Rengoku to become a demon. He says that Rengoku is obviously a Hashira at first sight, emitting a bright fighting spirit that’s been developed to the edge of perfection.
Akaza explains that Rengoku will never reach true perfection because he’s a human. People age and inevitably pass away, but demons can train for hundreds of years and become infinitely stronger.
Ultimately, Rengoku didn’t become a demon. He says that growing old and passing away is what gives human life meaning and beauty. These words are offensive to Akaza, who then enters a battle stance. If Rengoku will not accept the offer, then a fight is inevitable.
Rengoku and Akaza then engage in an epic battle. The Flame Hashira is forced to fight at exceptional speeds and use many different breathing forms and techniques.
Tanjiro, who can barely stand after receiving a severe stomach injury, tries to help.
Rengoku shouts at Tanjiro. “Don’t move,” he says. “If your wounds open, you’ll die! It’s not your time yet!”
Inosuke is also unable to help Rengoku due to the speed of the battle. As the fight goes on, Tanjiro and Inosuke are able to safely jump in when Rengoku’s arm goes through Akaza’s chest. However, it’s too little too late. Akaza is able to break away and flee the scene before daylight breaks.
Tanjiro is forced to throw his sword at Akaza, but isn’t able to deliver a final blow.
So that’s the answer. Tanjiro didn’t help Rengoku because he had a severe stomach injury. Rengoku orders Tanjiro not to intervene, saying his wound will surely open up and become fatal.