I don't know the details but wow!!
For a Japanese animated movie, this one tops the regular. Maybe it's the time of the production or the involvement or foreign studios. Either way the animation is top-notch, though there's a bit trouble with the lip movement of English speaking characters but that's probably because they might've been done by Japanese animators who had hard time timing the sink with the accent. Apart from that CGI sinks perfectly with hand drawn, even now until the day i write this review, December 25 2021 anime has hard time blending 3D with 2D. You could easily tell tell it's 3D, it's stands out and sometimes the CGI itself is poorly done, doesn't blend with the movements of the hand-drawn and moves more like a machine.
Oh yeah I almost forgot Kudos for not censoring the body of the corpse. Usually you know how anime is they'll censor everything.They're fine with lolicons but would rather die than show a bit skin when necessary. Great story btw I've yet to watch the anime, great side dish before the main course i guess 😉