Strike Witches was tasteful and restrained compared to this. Even the first season.
Sorry guys, but I’m going to have to judge this book by its cover, or to be more precise, this series by the first 15 minutes of the first episode, because that’s all I could take. Non-stop sexual innuendos about junior high girls is NOT cool.
The pre-OP didn’t give anything away, except that the primary quartet of girls appears to be English, American, Belgian, and Swiss guns. Japanese flavor comes from the high school, where the Belgian’s older sister attends. One head-scratcher is that they reference a Germanic teacher (“Stopping power is attractive”) with a Japanese name. In fact, they all seem to have Japanese names. (related to their actual gun names, as much as possible, but it’s disconcerting.)
Her next thought is that her hammer would fire all the time in those big hands. No, I'm not making it up.

Of course, his excuse for being in that position is that he was exhausted trying to climb the stairs, right?
So a couple of days later, he’s there for his first day, and the principal is giving him a walk-around. WHF still hasn’t gotten it yet. The observe a bunch of girls doing morning shooting practice, and FNC arrives late. Trying to remember her name, he finally goes, “Oh, the girl with the thong!” loud enough for everyone to hear. She promptly empties the clip at him. Several clips, in fact, hospitalizing him.
Where I finally threw in the towel was when FNC visited the school nurse about these funny “overheating” feelings she was getting, and the answer was yet another double-entendre about keeping her hammer lubricated… Then the next girl came in with a stomach-ache, and the doctor felt her tummy. “Oh, your spring is weak!” “Ah, so she jammed!” goes FNC. That was the straw that broke the camel’s back, it was just too dumb to put up with. I didn’t want to wait for that to be turned into something sexual, too.
I’m outtahere, and I recommend that anyone who doesn’t enjoy sexualized 13-year-olds do the same.
I mean, at least Strike Witches only stuck my nose in their crotches….
Edit: One more way this series comes up short vs. Strike Witches. In SW, the characters’ personalities stood out immediately, from Miyafuji’s ernestness, to Lucchini’s laziness, to Shirley’s brashness. Of course, those are largely caricatures of the national reputations, but it works. I’m not seeing that in Upotte! They’re bland — unless you want to talk about Belgian hammers. The closest they’ve gotten is when “America” grumbles “You Europeans!” and is promptly dragged into something she doesn’t want to bother with. I suppose the last forty years has been somewhat the opposite, though, so maybe they weren’t trying to make a joke.