Demon Slayer: The Hashira Unite Ending Explained - Tanjiro Kamado swears to kill the Demon King

The thrilling finale episode to the fourth season of Demon Slayer, The Hashira Unite, released on June 30th and it blew fans away with its fantastic animation and emotional dialogue. Here's delving into a detailed explanation of the ending, spoilers ahead!
The episode started off with a long and emotional discussion between Kagaya Ubuyashiki, the 97th leader of the Demon Slayer Corps and Muzan Kibutsuji, the Demon King and the leader of the Twelve Kizuki.While Ubuyashiki hasn't appeared much throughout the show as compared to the manga, the scene is still tense and cathartic. Kibutsuji has been trying to eliminate the Ubuyashiki family for years, after one of the previous Demon Slayers nearly killed him, and instilled a fear of the Demon Slayer Corps in him.
Ubuyashiki talks about the curse that has plagued his family's bloodline for years, causing their lives to end prematurely, although he himself has been able to stave off the effects of the curse for some time. Despite Kibutsuji challenging Ubuyashiki by entering his family's mansion, Ubuyashiki's weakened state prevents him from being able to properly fight and kill Kibutsuji, who mocks him for this. Meanwhile, the Hashira, who have learned of Kibutsuji's location, run for the mansion in an effort to save Ubuyashiki before the Demon King kills him.
However, the grim and melancholy mood of the episode is cut short when, half-way through, Ubuyashiki explodes the mansion into flames— a beautiful shot animated in slow-motion. Ubuyashiki and his entire family die in the fire, and even Kibutsuji is hurt, although he quickly regenerates.
The Hashira, who reached the mansion just before it blew up, are united by Ubuyashiki's death, and immediately begin fighting Kibutsuji together. The final battle lasts for the rest of the episode, a feast for the viewers since the rest of the season had been rather calm and had no demon duels. The Hashira use all their Breathing Style Techniques in tandem, but Kibutsuji shows off his own power by simultaneously sending all the Hashira to the Infinity Castle. The season ends with our main character, Tanjiro Kamado, swearing to kill the Demon King.
After the credits, the creators feature a Taisho Secret, revealing that Mitsuri was Kyojuro's tsuguko, and proceed to discuss Kyojuro for a few minutes, saying that he was passionate. This is cut short when the disembodied voice of Kyojuro interrupts them to tell them that it's time to fight Kibutsuji.
The final arc of the story, Infinity Castle, will be coming to theatres as a film trilogy where the Demon Slayers will finally challenge Kibutsuji and his demons. The release dates for these movies are currently unknown, but a trailer has already been released.