The structure of the Demon Slayer Infinity Castle movie is pretty much exactly what you’d expect; the Demon Slayer Corps, including the Hashira, Tanjiro, Zenitsu, and Inosuke, were transported into the twisting maze of Muzan Kibutsuji’s Infinity Castle in a desperate move to finally destroy the Demon King. Between multiple flashbacks (I counted 12 of them during my viewing), we get three impressive fights against some Upper Ranked demons.
They all look great. There is no denying that. Ufotable has performed some sort of wizardry to make these scenes pop. Give their animators all the flowers (and also a long period of paid time off) for delivering bigger and better than was reasonable to expect from them. However, as impressive as Shinobu’s fight against Upper 2 and Tanjiro’s battle against Upper 3 were, neither was as fun or satisfying as Zentisu’s fight against Upper 6. While everyone else fights for revenge, Zentisu fights and mourns a friend.
There are a lot of reasons why Zentisu’s fight in Demon Slayer Infinity Castle is so memorable. The visuals are just as stunning as everywhere else in the movie. The use of lightning effects with both combatants’ strikes adds to the sense of energy and movement. The pace follows the usual back-and-forth that Shonen fights usually have, with momentum shifting between Zenitsu and his enemy, a former friend who trained with him as a co-successor to the Thunder Breathing school of swordsmanship.
It is this relationship that stands out among the other fights in Demon Slayer, which are also broken up by multiple flashbacks to flesh out the story and give pathos to the non-stop action on screen. There was a time, before the events of the Demon Slayer manga, when Zenitsu and Kaigaku were students together; brothers and rivals for a place as successors to the Thunder Breathing school. While this trope is overused at times, it frames this fight differently from any of the other fights in the movie.
But there is also something beautiful in the way that Zenitsu wins this fight that, as someone who has studied martial arts, spoke to me. Zenitsu can only do the first - and most basic - form of Thunder Breathing. Kaigaku can do everything but the first form. He loses because he lacks the fundamentals, the structure upon which everything else in the school is built. It is like being able to do a wheelie on a bike without learning to ride it normally; sure, it looks impressive, but it is woefully impractical and actively gets in the way of your studies.
