Bungou Stray Dogs is a manga and anime about famous literary figures who've been reincarnated (?) in a 1920s-themed version of modern Yokohama, Japan. With superpowers. Some work for the mafia and others are in a detective agency, with some pooling between the two groups.
The TV show's pretty good. I enjoyed its first two seasons, both in 2016. This film followed in 2018 and there was a third season in 2019, with another film confirmed in March 2020 to be in development. After watching this film, though, I deleted my copies of the Season 1-2 episodes. I probably won't bother watching Season 3. However I'd have probably enjoyed it if I'd preceded it with a big rewatch of all the 2016 episodes.
The film's problem, I think, is that it's leaning too heavily on the story so far. If you've got everyone's backstory at your fingertips, you'll care. If you haven't, you won't. The plot structure's a bit vague, setting up a big apocalyptic threat and then sort of letting its cast wander around in it. It's all a bit genteel and laid-back, despite the fight scenes. Stuff sort of happens. Oh, look, some violence. The significant cast members are:
(a) an idiot who protests that it's wrong to kill the mass-murdering supervillain and that it's unthinkable that Dazai might have betrayed his friends.
(b) a drab female killer who's good at fighting. (She's more interesting in the TV series.)
(c) a drab male killer who's good at fighting. (This should theoretically be startling, if you've seen the TV show and remember what a monster Akutagawa was. Here, though, he's bland.)
(d) the suicidal, off-handedly brilliant Dazai, who's still the most interesting person in the show. Unfortunately, though, he suffers from the same "I don't care" problem. His plot role here would have been extraordinary and compelling if he'd been someone who cared about danger and people's lives (including his own), but instead he's just drawling his way through like Oscar Wilde on extra opium.
The supervillain is just as laid-back, incidentally. Try to kill him and his underreaction will, at most, be a shift to a slightly different kind of languid boredom.
The fights are well animated. They're also a bit dull, but hey. Our heroes are pitted against their own special abilities, which is lame for two reasons. The idea itself I'm fine with, but the superpower-spectres have been given a fragile weakness that undercuts the threat. I was also mildly distracted when someone said, "No one can win against their own special ability!" (What if I had the power to make your toenail clippings turn purple?)
This film makes a good show look bad. It'll be almost impenetrable to anyone who's new to the franchise, but not because it's hard to understand. That's not the case. It's quite straightforward, in its meanderingly written way. Instead, it's hard to care. Feel free to watch it in its appropriate place if you're watching all of Bungou Stray Dogs in order, though.