Warning: Contains spoilers for Jujutsu Kaisen and Jujutsu Kaisen 0.
The way that Jujutsu Kaisen 0 is structured allows it to avoid the biggest problem that Demon Slayer: Mugen Train had. Both movies were the latest installments to come out of Jujutsu Kaisen and Demon Slayer: Kimetsu no Yaiba, respectively, but each of the two films relate to their franchises in different ways. Mugen Train’s relation to the wider Demon Slayer series ended up causing some problems for both viewers and season 2 of the anime — but the way that Jujutsu Kaisen 0 does things makes it far less likely for the same issues to emerge.
While most anime movies are essentially noncanonical filler, Demon Slayer: Mugen Trainwas a direct continuation of where Demon Slayer season 1 left off, and as successful as the film was, that still resulted in some problems. Since the movie was the latest installment of the story, that made it essential viewing for the anime, so anyone who didn’t see it would be completely lost on what was happening. Demon Slayer season 2 tried to work around this by spending its first half recapping Mugen Train, but that was criticized by many people, as well. Mugen Train was written to be viewed as a movie, and Ufotable’s attempt at breaking it up into a single hour of anime resulted in the pacing slowing to a crawl, which made people wish that they had just skipped right to the Demon Slayer Season 2 «Entertainment District” arc, especially since the original movie was already available for streaming and would see a physical release not long after Demon Slayer season 2 began.
Related: Demon Slayer Season 2 Is A Great Mugen Train Sequel (Because It's Its Opposite)
Mugen Train’s placement in canon caused a variety of problems for both
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