The 9th episode of Upotte is a beach episode that turns into something entirely different by the end of the episode. The girls are whisked away to a seaside city where the usual antics of beach and onsen episodes take place. Then, things take a dramatic turn as a group of shooters begin attacking the girls and then the city indiscriminately. The episode ends with the main cast preparing to counterattack as the city lies in flames.
This was one of those episodes that was a tale of two halves. The first was the typical low-brow comedy that is typical for this series. The second half became serious drama, especially since real people get involved in the conflict.
The first half like I mentioned earlier was really just your average beach episode. There are the jokes about swimwear matching the guns, and perverted antics that are thankfully obscured by the mysterious fog of censorship. We are also introduced to a new character in G3’s younger sister HK33E, who also doesn’t appear to have a nickname she doesn’t hate.
As for the jokes, there are still quite a few that are worth noting. HK33 managed to shoot through the apple on the cover of SG550’s copy of Wilhelm Tell. Obviously the only reason she was reading it was to set up that joke. When the group got to the top of the castle on the hill, I did like that M16 and SG550’s first reaction is to start practicing some shooting because they just sightseeing wasn’t their style. Also, as the plot kicked in, there was FG42 looking like an entirely different person in street clothes sans eye patch which caught Insert-sensei asking who she was. Overall, the meta joke worked, but the beach stuff was a waste of time.
Then, as for the 2nd most outrageous genre shift of the week, came the moment when everything came under assault. Seeing the girls under attack is nothing new, and it’s never really had a semblance of threat. What changed is that this became a full blown terrorist attack on the city itself. Yet, there is a remarkable level of restraint shown as this is happening.
Insert-sensei actually gets shot, but he only walks with a limp, rather than displaying a more visible sign of having been shot. Even around the areas where bombs are detonated, there are no people caught near the explosions, only those around to observe the aftermath. I can only really think of this as a way for the plot to remain tied to its genre. The humor would simply disappear if there were suddenly characters getting killed by terrorists.
In a way, I believe that makes this entire arc seem like a bad idea. The simple beach episode aspects of this series are enough to ruin just this episode. This terrorist siege ruins the series as a whole. Perhaps I am over-thinking this plot turn though and nothing bad will actually seem to happen next week.
As for what I believe is the final episode (though I believe there is an OVA later this year), I think it’s setup that this actually was the training exercise they were talking about early in the episode. Jokes will fly as the two sides fight each other before FNC saves everyone. It’s not like Insert-sensei is going to take a bullet for her again.
Lower Mid-Table 
Actually this is the shootout I’ve mentioned both on Twitter and in my previous replies here. The setup is certainly different though (it DIDN’T continue from the seaside class), but it’s certainly as you noted: it’s treated in all seriousness by EVERYONE involved, and escalated to the point where Ms. Thompson and the submachinegun kiddies had to join in.
Interestingly enough, the manga hints that this just isn’t a grudge match between Seishou and Akaganeko (the school of the AK variants), as AR-18’s cousins HOWA Type 64 and 89 and Saiga (the shotgun based on the AK) also get involved, but the latter three aren’t aligned with either Seishou or Akaganeko.
It’s way too large to be a grudge match. I’m actually surprised FNC still seems to be the main character when all of the plot events seem to center around M16 and how the others get involved.
There is a lot of mood shifts in the manga. On the one hand, it’s a slice of life about Gun Girls that we could compare to K-On. On the other, we can see why it’s published as shounen when the gunfights start. But I would argue the mood shifts are done successfully. The story arcs are really short and there is, initially, 2 or 3 chapters where the villains are introduced.
I can understand shifting genre to spice up the story, and the fact that it is about guns makes it a good idea for a shounen gag manga. I think this was only the 2nd time the mood of the story has changed though. In my opinion, I don’t think it’s earned the right to turn this extremely though.