An all-boys school goes co-ed and literally a week later, an alien crash lands and spills all her genderbender juices over the student body, oh no! Now, next to the few natal girls that are yet unicorns, the school instantly became an all-girls school! Well, until the only guy who escaped this mishap (?) arrives ... The ultra-fun premise is better than the execution. Unbalanced School Life is decent, but this manga doesn't know what it wants to be. It's a 2 volume 15 chapter series, but the pacing is weird as hell and the manga pretends it has the luxury of pacing like a 8volume or more school life romcom. There is an entire chapter of going to the mall, and another about some POTENTIAL (not even definitive, just potential) love interest giving the MC (the remaining male) private tutoring. These two chapters alone account for one seventh of the total runtime. Besides, these two chapters also didn't make use of the premise: they are between a guy only into "real girls", and a naturally-born girl. These mentioned episodes could have been in any school SoL manga.
These two characters aren't even that interesting) when you have a literal entire school that could explore the genderswap aspect (which has also shown to have a few more interesting characters, like Midori). Allow me to channel my inner logistics nerd, but this setup is so fruitful, they could even make a couple side stories about how the school adapts to the change (e.g. looking what sports gear still works, and what has to be newly ordered).
The plot thread of finding out who is a "real girl" and who is an ex-boy could also have stretched throughout the entire manga, instead of being resolved immediately.

This natal girl that serves as potential love interest isn't alone: the MC's current crush is on his older childhood friend, who is the school nurse (being like 8-10 years older), and it's hinted that also his same-age boy childhood friend (now neo-girl) might either be interested in him or he in her. So it's a veritable love polyhedron. But manga, you can't really afford this. You are just 15 chapters long.

The most interesting few pages is when the MC asks his natal female potential love interest if she considers the neo-girls to truly also be girls. She is painted as a bit a stuck up person, but also "proper", so normally you would expect her to say something like "Of course! Their minds may have been originally male, but now we face the same struggles in the world." or something to that effect; or on the other hand "I can't. Not yet. I can't ignore that they were teenage boys with certain urges and mindsets until recently. I need to have more time, and see more willingness from their side to adapt."
But instead she snaps at him and goes on this yikes speech of "Haah??? Why should I do that? They are clearly still boys, even if they look like girls. Just look at how they act!" and we see a scene how the ex-boys still horse around exactly like boys. Not merely tomboyish girls, but truly like boys would.
And the speech itself not, but what it points to, made me so pensive and melancholic.
I can hardly explain why. This feeling is partially one of beauty: no matter what happens to you physically, you are still you. The mind is not so fragile that it can easily be overwritten.
Then there's the element that the ex-boys do not let their new state take away the joy in life. They refuse to let that happen. We just have to keep living, no matter what lies in our past.
Partially, the feeling was also one of sadness that despite or precisely *because* what I just mentioned, it is simply the case that these boys now have a new corporeal and social reality to deal with, and this scene here of them rough-housing around in a field, is a peak of their remaining boyhood. It can only go downhill from here. Every day, they will be a little less the boys and men they were.

There are even more such emotions to that scene, but anyway, enough with the melancholy.

Another story beat is that the neo-girls become aware that integrating a proper male into their dorms (including bath access) is perhaps not as mentally easy for them as they thought it would be. They feel apprehension that he is truly a guy, and they are girls, and he could do many, many things with them if he wanted. Of course this is all framed as purely a coolheaded, logistical debate, not one where psychology already plays a major role (as they still, naturally, all feel like guys) -- but that may lay in their future.
But who really cares? That plot point is dropped as fast as it's brought up. As said, because this manga has bizarre pacing.

The ending points to this series being told to prematurely wrap up, or the author just losing interest. But even the last volume still has that weird pacing issue so I'm not sure if it's the former.

Honestly this manga should not exist. Not because its idea and concept is unappealing. On the contrary. But because it's a fantastic skeleton for a much bigger story, in the vein of Love Hina or Boku Girl and other such genre heavyweights.

Recommendation: read if you are into gender bender.

A vaguely, very distantly related manga would be Ame Nochi Hare, about students that switch gender whenever it rains.