It's actually quite good, once it gets going. However it's not as convincing or hard-hitting as it could have been, while you'll get irritated if you compare it with its parent film. It's supposedly a "spiritual sequel" to the 1981 cult classic. What does this mean? The answer seems to be "resurrect everyone who got killed, turn Izumi's yakuza into comic relief and dumb down all the backstory and motivations."
Sailor Suit and Machine Gun (1981) had a schoolgirl, Izumi Hoshi, reluctantly inheriting the leadership of the Medaka yakuza gang. They're a menacing bunch of thugs in a scary underworld. This leads into a gang war that's heading for a high body count. Izumi discovers unwelcome truths and goes on a pretty huge character journey, not always in reassuring directions. The film ends with the Medaka gang no longer in business and Izumi going back to being just a schoolgirl.
This film, on the other hand, has the Medaka gang still alive and having renounced their life of crime under Izumi. They're running a Medaka Coffee House. There are three of them. Takuro Ono is a pretty boy who probably sings in a band. Shohei Uno is even more adorable. Tetsuya Takeda's the only one who looks even halfway convincing as a gangster, but he's also nearly seventy years old. (We also see flashbacks of Izumi's late uncle, who was a father figure to her and looks even less gangster-like than she does. He's a beautiful old gentleman. If he stood for election, you'd vote for him.)
Annoyingly, the film's other gangs are well cast. There are plenty of yakuza here who look thuggish, scary or even psychotic (Masanobu Ando). It's just that the casting director chose none of them to play Izumi's henchmen.
Similarly, Izumi's character journey up to now has been flattened and dumbed down. We also see two flashbacks to a reshot version of the 1981 film's most famous scene, making it doubly obvious that she's holding her machine-gun incorrectly. The only thing she'd have hit would be the ceiling.
Tonally, this film's on a conveyor belt. Act One is lightweight. I wasn't scared. People tend to be prettier than they were in 1981. It doesn't feel like a serious portrayal of the criminal world. There's an irritatingly bad sequence where a schoolgirl on drugs runs into the road and gets killed. (On paper it's fine, but the director's choices are robbing it of the weight it deserved.) I'd also be cursing the film whenever it cheapened its own backstory, although that's my fault for watching it back-to-back with the original.
Later, though, things gets harder-edged. Izumi stops hanging out with the Medaka gang and makes some less cuddly allies. In short, the film becomes reasonably good. Stick around and you'll see a bloodbath. Izumi learns who killed her uncle, which is a cliche but plays out more compellingly than I'd expected.
It never becomes a first-class yakuza film. However it does get up to "not too bad" and "reasonably watchable".
To be honest, I'm convinced that the Medaka gang were a late script addition. They hardly do anything anyway. Resurrecting them is a counter-intuitive decision in a sequel (sorry, "spiritual sequel") and it would have been a trivial rewrite to remove them. Imagine that hypothetical film and you'll see a colder, darker, harder flick. That would have been better, to be honest. The Medakas are pulling this towards a Children's BBC version of the material, but it must be said that they add warmth as well.
There's a charming scene, quite late, where two of them are hanging out at the cafe with Izumi and talking nonsense with her. Sometimes that felt improvised, but in a good way.
The film's trump card, though, is Izumi herself, played by Kanna Hashimoto. It's always fun to see this tiny schoolgirl talking tough to gangsters and behaving as if she owns the place. (She's five foot nothing, for what it's worth.) Hashimoto does pretty well in the role, I think, and I'm quite pleased to see that it won her the Newcomer Award from the 40th Japan Academy Prize. She hasn't been given the complexity and character journey that Hiroko Yakushimaru had to play in 1981, but there's something there (e.g. indications of how she feels towards sex) and a half-hearted performance could have sunk the film. Viewed objectively, after all, it's pretty silly. She's a schoolgirl. In a realistic film, she'd have been eaten alive.
You wouldn't call this an impressive film. It's certainly not a classic or anything, which puts it well below the original even when they're hitting similar beats. Instead it's just fun and it works pretty well, once you're past the slightly tiresome early scenes with the Medakas. They're not disbanded or dead. That's just wrong. There's also a weird preachy scene where a villain blames everything on the younger generation for not looking after their parents and so leaving the field open for organised criminals.
I can't bring myself to call this a good film. It's too uneven and I can't give a free pass to the Medakas, but even so a lot of it's pretty reasonable. If you watch it, you'll probably enjoy it.