Cut through the night where demons dwell!
Four months have passed since the death of Rengoku. With their spirits still blazing through, Tanjiro, Inosuke, and Zenitsu accompany the Sound Hashira, Tengen Uzui, on a mission to Yoshiwara to help search for his missing wives who were investigating rumors of demons within the district.
Tropes associated with the Red Light District Arc:
- Abusive Parents: Daki and Gyutaro's mother, who beat her children regularly.
- Affably Evil: Kokushibou, the Upper-1.
- Arc Hero: The Sound Hashira, Tengen Uzui
- Arc Villain: The Upper Moon 6, Daki at first. It later turns into a Big Bad Duumvirate with her older brother, Gyutaro, who's actually the true holder of number 6.
- An Arm and a Leg: Uzui loses his left arm and eye during the final battle.
- Attractive Bent-Gender: Of the three who had to dress up, the unmasked Inosuke accomplishes this trope the most. It helps that Tengen ordered him not to even try to fake a woman's voice, let alone speak.
- Even Evil Has Loved Ones: Unlike Rui and Enmu from the previous arcs, Daki and Gyutaro genuinely care for each other, and do their best to protect the another. Even when they argue on the brink of death, Tanjiro sees through them and assumes their bond.
- Bittersweet Ending: Daki and her brother Gyutaro have been slain causing a major upset in the demon hierarchy for the first time in a century and giving the Demon Slayer Corps hope of defeating Muzan, Tengen barely survived the fight thanks to the Demon Slayers' assistance, and his wives are still in one piece. However, the Yoshiwara district is totally wrecked in the process, and Tengen is forced to retire as a Hashira due to the injuries he sustained from battling an Upper Rank member of the Twelve Kizuki.
- Bond Villain Stupidity: Daki should have checked Tanjiro and Nezuko were dead before wandering off.
- Similarly, the arc (if not the series) could have ended very differently, hadn't Gyutaro wasted his time in attempting to recruit Tanjiro and just killing him outright.
- Break the Haughty: Akaza isn't having a great time after his loss to Kyojuro. Despite killing the Flame Hashira he had to run away from the sun with his tail beneath his legs, got called out as a coward by Tanjiro who told him that Kyojuro was the true winner, and Muzan tells him that his performance was pathetic since he only killed the Hashira and not the other three Demon Slayers there. Suffice it to say Akaza is pissed after being chewed out by Muzan and promises to pound Tanjiro's face into paste the next time he sees him.
- Children Are Innocent: The afterlife judges Gyutaro to be the corrupter behind Daki, and initially allows her to go to Heaven. She changes her mind once Gyutaro goes to Hell.
- Dual Boss: Once Gyutaro comes out of Daki's body the two proceed to fight the Demon Slayers together. It's also revealed that part of what makes the fight so difficult is that killing just one of the siblings won't do any good, the only way for them to truly die is if both of them have been decapitated at about the same time, otherwise the other will just reattach their head. This eventually leads to the fight splitting up with different members fighting Daki and Gyutaro at the same time.
- Happily Married: Zenitsu is shocked and enraged that Tengen has three Kunoichu wives. It is revealed that he wanted them to look out for themselves while he vows to look out for them. They had since devoted themselves to him.
- Heel Realization: Gyutaro has a poignant one as he realizes what he did to his own sister just to improve his standing in Yoshiwara.
- The Heavy: Daki served as the main threat in the story, as she was responsible for capturing Tengen's wives and was causing a lot of trouble in Yoshiwara. Then during the fight between her and Tanjiro & Nezuko, she managed to stand her ground pretty well and did significant damage to them. That is until they Power-Up that she begins losing control of the battle. When Tengen Uzui arrives and easily decapitates her, she gets upset and calls for her big brother, Gyutaro, who's revealed to be the true Upper-6 demon.
- Hidden Depths: Zenitsu happens to be very skilled in playing the Shamisen, which impresses the members of the Kyogoku House.
- Hidden Villain: Gyutaro, the true Upper-6.
- Honey Trap: How Daki 'collects' their food.
- Minor Crime Reveals Major Plot: Tengen's wives missing in Yoshiwara -> Daki and Gyutaro laying a trap to kill the Demon Slayers.
- New Powers as the Plot Demands: Nezuko has gained the ability to shape-shift into a more powerful demonic from, as well as using her Blood Demon Art to manipulate her blood so she can still be connected to her body parts after they have been separated and harmlessly burn lethal poisons from peoples bodies.
- Tanjiro also unlocks his Demon Slayer Mark in this arc.
- O.O.C. Is Serious Business: Akaza, the Affably Evil murder-happy Demon from the last arc, is shooting Death Glares at Douma and Kokushibou during the meeting of the Upper Ranks.
- People Puppets: What Gyutaro's Blood Demon Art amounts to. He can also control Daki with them better than she could control her own body.
- Psychopathic Manchild: Daki and her temper tantrums resulting from jealousy. Justified, because she was turned at age 13.
- Retirony: Surprisingly averted in regards to Tengen. A flashback shows that Tengen's wife Hinatsuru made Tengen promise to retire from demon slaying after killing an Upper Rank level Demon. Despite the heavy injuries he received, and what happened the last time a Hashira fought an Upper Rank, Tengen makes it out alive and decides to retire with his wifes.
- Screaming Warrior: In both dubs, Tengen and Gyutaro scream their hearts out in the final phase of the fight. Tanjiro, Zenitsu, and Inosuke join in soon after.
- Sharing a Body: Daki and Gyutaro do this to fool the Demon Slayers.
- Time Skip: Narration notes that, in-between Rengoku's death and the trio being recruited by Tengen for the titular mission at the Entertainment District, four months pass during which time Tanjiro, Zenitsu and Inosuke train and go their separate ways on their own missions.
- Together in Death: Daki decides to go to Hell with Gyutaro, rather face eternity in Heaven alone.
- The Unreveal:
- Tanjiro arrives at the Rengoku residence in order to offer up Kyojiro's last words and find out about the secrets of Sun Breathing. However the book that might have contained such information was destroyed by Kyojuro's father some time ago though Kyojuro's brother promises Tanjiro that he will look into it see if he can discover any more secrets about the technique.
- While we eventually learn that Daki's human name was Ume its never revealed what Gyutaro's original name was.
- Wake-Up Call Boss: Daki and Gyutaro (but especially the latter) prove to be this to a greater degree than Akaza, as they nearly manage to kill all the Demon Slayers there, only failing due to a mistake on Gyutaro's part.
- Wholesome Crossdresser: Tanjiro, Zenitsu and Inosuke dress up as women to infiltrate the Entertainment District.
- Would Hurt a Child: Daki's village residents burned her alive for attempting to save herself from a samurai. She was 13 years old.
- Wrong Genre Savvy: Gyutaro should have thought twice before asking Tanjiro to become a Demon.
- You Are Worth Hell: An literal example of this, as Daki willingly gives up her chance to go to Heaven in order to stay by Gyutaro’s side as he’s sent to Hell.
- You Have Failed Me: Muzan considers doing this to the Upper Ranks, after Daki and Gyutaro's deaths. He decides not to do so.
