I doubt anyone will listen to this but I have so many thoughts about Kyojuro Rengoku in Demon Slayer and how he was written and how he ended up so here’s your warning before the read more:
🔥‼️MAJOR SPOILERS AHEAD FOR MUGEN TRAIN ONWARD‼️🔥
With that out of the way…
Kyojuro Rengoku was written to die and is intentionally used to tug at heart strings while simultaneously inspiring other characters after his death.
It’s not something I see people talk about often. They say his death was tragic and awful, and it absolutely was. But, he was absolutely and without a doubt written purely to be killed off. In the anime they make it exceedingly obvious between one of the lines of dialogue he has in the first episode of the Mugen Train arc (an addition to the story that’s not in the manga):
“I promise to tell my father I came across you two. I’m sure he’ll be thrilled.”
To his imagery in both the OP and the ED of the season.
In the OP, Rengoku faces right instead of left in the title card, which until the Inifinty Castle arc will be the opposite for every other character who faces left with Tanjiro. These other characters don’t die in their respective arc.
In the ED (this is legit the only shot I could get I’m sorry ;-;) Rengoku is surrounded by imagery of spider lilies. In Japanese media, more often than not characters associated with spider lilies will die at some point in their series if not incredibly soon.
But again these were exceedingly obvious on the part of the animators. They intended to make it clear that he was going to die, even from the start. I’m not even gonna get into his entire death scene because I am never strong enough for it (and everyone already knows “set your heart ablaze”) so let’s skip ahead to after his death when Tanjiro goes to visit the Rengoku family to impart Kyojuro’s last words and investigate the writings of the previous Flame Hashira to learn about Hinokami Kagura. While there, he gets into a spat with Shinjuro, Kyojuro’s father, about how he was physically abusive to Senjuro, Kyojuro’s younger brother, and learns that Shinjuro destroyed the notes in a drunken state.
The only thing that gets Shinjuro to change to better himself and to stop drinking is when Tanjiro tells him Kyojuro’s last words for him.
“Take care of your body.”
It’s the one and only thing to get Shinjuro to change. After that, Senjuro gifts Tanjiro Kyojuro’s sword guard to put on his own sword. It doesn’t come into play until the Swordsmith Village arc, but there’s more before that.
Later on in the Entertainment District arc, Tengen says he could never be like Rengoku and asks how he would fight the upper rank demons, to which Rengoku’s spirit responds;
“I could never be like you, either! Your sword skills are a thing of beauty! Though you do have too many wives!”
But after this he adds, “Look after Young Kamado, the yellow boy, and the boar head boy for me, Uzui.” before fading away. Tengen afterwards is inspired and does what his friend asks.
In Swordsmith Village, Rengoku is almost wholly unmentioned besides his sword guard, but it comes into play with Tanjiro asking it be added to his sword and later on that it saves Kotetsu’s life. Muichiro sees and cries remembering Rengoku, and when Tanjiro hears this, he tears up and thanks Rengoku for saving another life even after death.
Finally, in the current season of the anime Rengoku played a very small part in one of the Taishō era secret sections at the end of the episode where they encounter Muzan. They’re talking about how Mitsuri trained as Rengoku’s Tsuguko and how his training was brutal but fun when suddenly they hear his voice. He’s offscreen and when he speaks Mitsuri and Tanjiro look offstage to see him but when the camera changes he’s gone.
“That’s nostalgic. I remember it too. Finally, the time to fight Muzan Kibutsugi has come. I’m counting on you guys.”
After he speaks, Mitsuri says “Rengoku was just there, wasn’t he?” and Tanjiro affirms her question.
(I can’t add anymore photos after those so take my word for it from now on.)
The last bits of post death Rengoku lore that I remember is thus:
During the Infinity Castle arc, Tanjiro and Giyuu fight Akaza. Tanjiro wants revenge for Rengoku’s death, especially after Akaza insults him which results in iirc the first instance of Tanjiro swearing angrily at someone saying, “What did you say? You. You ass. Don’t talk about Rengoku-san.” During the fight, Giyuu almost falls victim to the same attack that killed Rengoku, but Tanjiro learns a new breathing technique that allows him to slash Akaza undetected.
Shinjuro is tasked to help protect Kiriya Ubayashiki with Tengen.
When Tanjiro is trying to fight becoming a demon, Rengoku, who had told him to hold his head high when he’s feeling disheartened and can’t go on, holds his head up the highest to allow for his friends and family to bring him back to humanity.
Senjuro and Shinjuro visit Tanjiro and co. in the Butterfly Mansion after the final fight with Muzan as he’s recovering.
And finally, the biggest one, at the very very end of the series after the timeskip with all the descendants and reincarnations of characters, Senjuro’s descendant is the reincarnation of Kyojuro, named Tojuro, and he’s the best friend of Tanjiro’s descendant and reincarnation named Sumihiko. Tojuro is the last of the descendants/reincarnations to be introduced, and the final panels are the two of them running to school together.
A good character comparison to make to Rengoku I think would be Maes Hughes from Fullmetal Alchemist/Brotherhood. He’s a very sweet, outgoing family man who loves his family more than life itself and who the main characters attach to as a parental/older sibling figure. Their influence throughout the rest of the show is clear and impactful and many things wouldn’t have happened unless they died. They were both characters written to be killed off and for their presence to tug on the heartstrings any and every time they’re brought up after their deaths.
Sorry for the wall but I’ve been dying to talk about this.
