...I am amazed. It's been such a long time since a yuri visual novel has reeled me in this hard, and I am GLAD that it does, because it gives me hope for quality yuri products like this in the future. This is more or less my feelings toward the game rather than a review. Honestly I'm going to recommend it either way, but here's my ramblings if you're interested.

The title is exactly the entire plot of the game. I meant it. The title, is a spoiler, by itself. The summer romance literally bloomed from a lie. Actually, it's more than one lie. Everyone lies, and they essentially connected Kaoru and Shiori together.
This game's plot is "deceptively simple" because it's built on the complex premise of every characters, their backgrounds and their relations to the two main couple the game focus on. Because of how short the game is (20~ ish hours of reading) it works out beautifully without dumping on you with unnecessary plot. Nothing was dragged out, the explanations don't take you 27 chapters of Jujutsu Kaisen. This is one of the thing that, you as a yuri fan needed to experience by yourself to know how much yuri has changed from the dramatic soapland opera since the anno domini 2000s. It's basically "straightforward romance yuri with occasional drama and a lots of developments from the main couple to the side character, with a happy ending for everyone, even if some characters' ending are bitter more than happy."

As for the quality of everything else, this has to be the cleanest modern yuri visual novel I've ever seen. The sprite works look lively, every single one of them is animated beautifully and rarely do I ever felt uncomfortable while they're doing their stuff. This extends to THE CGs. It's very unique. The characters only have a few gestures, although not like they needed more, as animated CGs were the bigger contribution to visual quality. Not to mention, the voice acting is really great. REALLY great. Especially Kaoru's voice actor. Fitting for a big dork like her. Majority of the cast was voice acted by popular and talented JP voice actress, and it really surprises me when I recognize some of the names on the VA list, like Shiori's VA being the same VA for Euphy in MagiRevo, lmao. For the music, I've readed (unironically, yes) a lots of yuri visual novels from Western to Eastern, and there's only one or maybe two that the music doesn't grate my ears to the point that everytime I am reminded of it, my head couldn't think of anything but the absolute hell that is generic romance visual novel music that plays in my head for 10 hours straight despite me knowing that I can turn it off at any given point. Instead, it's very relaxing. It's more like that one ASMR lofi beat stream or some crap you listen to everyday before collapsing on the table while doing homeworks at 1AM in the morning.

Now, as I'm heavily biased about yuri, there's a few problems I've had with UsoNatsu. They're relatively minor and honestly the average consoomers won't be complaining about it, but I am severely, SEVERELY autistic and I pay attention to every details about the things I love, so I have to point out some of them.

1) This is probably one of the few visual novels that is developed on something that does not start with R and ends with y, probably for the better. Now that sounds good, but unfortunately... It's developed on Unity engine. The developers have nothing to do with this - the engine itself is just pretty dogsh!t. That's all. Unsurprising when one scene makes the game go from 60FPS to an instant 12FPS for no reason despite me running on the modern spyware.
2) "...it works out beautifully without dumping on you with unnecessary plot" is what I said, which is true, but there's one thing that basically contradicts my point, and it's the flashbacks that the game usually brings up at a certain point as to remind you of that. This is fine until you realize that this game requires you to remember a LOTS of things as the plot progress. This goes against the point of you having to remember them in the first place as this imply having flashbacks mean you already forget about what the hell happened in the story earlier even if it was just only two chapters ago. If you're having short term dementia that might help, but honestly it's just really annoying because everytime it happens, the game jumps back to the EXACT same scene, which for some reason lags the game and it is really irritating when they do that.
3) Audio mixing. Might be the worst problem the game has and it holds back the amazing voice acting in this game (only a portion of it). Sometimes it feels like a char is whispering in scenes that they're talking normal. Sometimes the volume goes up and my ears instantly bleed because it just happens to be a scream which I am not expected and because of the audio mixing, I have to put everything at maximum to hear scenes that their volumes were, for some reason, lowered down. Thankfully, this only held the voice acting back partially; like I said, due to how rare it happens.

In conclusion, I love UsoNatsu. In my opinion, this is a perfect example of how far the production of yuri visual novel has become since the recent years. There was no more of the generic trait that old visual novels used to have, everything looks clean, and there's more unique CGs and sprites being animated in a lively way compare to static sprites back then. It has every set standard that romance yuri should have nowadays, and it handles the specific problems that have appeared in yuri before pretty well and avoids mistakes that drags out the plot for too long and loses its charms, ending the story on a very high note for the couple.
It's a good treat for yuri fans, we deserved it. The score is subjective. There will be drama CDs coming soon, I don't know if it will ever be available on Steam in English, but we will see. Please buy this. Encourage them to create yuri VNs like UsoNatsu, because at the end of the day, quality is always better than quantity, especially when it comes to yuri in recent years when it gets popular as more bad works appeared and ruins the quality of yuri as we see it today compare to a few years ago. Might be me speaking as a boomer, or whatever the zoomies call it nowadays.