WARNING: The following contains major spoilers for Episode 12 of Deca-Dence, "Decadence" now streaming on Funimation.
After taking control of the fortress, Kaburagi is primed to take down the big boss Gadoll. However, things don't start off smoothly, as he finds himself involved in a philosophical exchange with the Deca-Dence system itself. He discusses the nature of bugs and resolves to change the world. The system, while a bit of a pessimist, allows him to give it a go. Meanwhile, the Gears and Tankers band together to retrieve old Deca-Dence parts, which allows them to put together a brand new cannon. With the new artillery strung together and some Natsume-related flashbacks on the backburner, Kaburagi powers up, breaks the Deca-Dence limiter and goes full-force at the big boss (while, naturally, the opening plays in the background). There's a huge explosion, the Gadoll disappears and the apocalypse is avoided -- everyone is saved. The fortress then comes apart, burying Kaburagi in the rubble and taking him out of the show properly... for all of 10 minutes.
The animation is on point throughout. In fact, the episode's climactic action sequences have some of the best visuals so far, producing a proper eyegasm during the show's final dose of Gadoll-punching mayhem. After some digging around, Natsume and the gang discover Kaburagi's body. He's sacrificed himself for real this time, so a teary thank-you is in order. With this said and done, Deca-Dence skips three years ahead to show how the world has changed.
Three years on, Minato is the new system administrator, and Jill is his secretary. Hugin and the game police are no more -- they disappeared when things got dicey. In the place of the oppressive Deca-Dence fortress is "Deca-Dence City," a "compound entertainment facility" (basically a theme park) where humans and cyborgs alike can have a great time. Built from the Deca-Dence ruins, the facility offers a long list of recreational activities. There's a farming game, zero-gravity dodgeball, a battle stadium and even a Gadoll area, where the once-bloodthirsty beasts have been transformed into cute, spongy familiars. The residential area has also been reworked, providing improved living arrangements for the Tankers. Briefly, fans are allowed to dip their toes into the new Deca-Dence, watching the cast live rosily in their utopian city.
Natsume now works as a tour guide, driving and flying around outside the city. She keeps a picture of herself and Kaburagi, along with a little Pipe keychain. Pipe, unfortunately, was not revived, but someone has evidently taken advantage of the disintegrated Gadoll's merchandising potential.
While Pipe stays dead, Kaburagi does not. Browsing through some old files, Jill discovers a backup of Kaburagi -- which is apparently a thing -- meaning he's able to be brought back to life, and he inhabits his original avatar for nostalgia's sake. The anime comes to a close as Natsume finishes one of her tours, sighting a Kaburagi-shaped silhouette in the distance.
It's strange having Deca-Dence end so quickly. The anime original was so dense and fast-moving that twelve episodes felt like hardly enough, though that isn't to say it didn't make the absolute most of its run. From the wild second-episode twist to the quirky video game premise to the wholesome character dynamics to the hurried world-building, Deca-Dence was attempting a hundred things at once -- some of them faulty, but none of them boring. The final episode encapsulated this wholly, blending everything together and creating a satisfying ending. Considering the positive reception, Studio NUT can go home happy with this one.