Setting
In a world with no sun only a limited man-made sun shines, there are giant insects seeking the "heart" of people and letters, so "letter bees" are tasked with the dangerous task of delivering the letters.

Story
It starts being Lag Seeing, who had his mother taken from him, being delivered as a "letter" to be taken care of, from that point onwards he decides he wants to be a letter bee too, and wants to deliver letters as well as find his mother.

Art
The line art is generally good, I'm not a big fan of high-contrast shading, but it doesn't bother me much here. Though generally, the author will bring some weird looking asses and disrupt the tone of the manga (as well as my appreciation for the manga in general).

Spoilerless review
While I didn't like it at all, I can see others enjoying it, and the best way to judge it is probably to read 2-3 volumes, if you don't like them, I doubt you'll like the rest, but if you like them, you'll probably like the majority of it.

Personally, I wasn't really invested in the main cast of characters nor the bigger plot, and the bad people from the short stories lacked any nuance whatsoever, mostly there for some cheap tragedy or revenge porn - which might appeal to some, but I found underwhelming.

The fights, while competently drawn, lacked any tension to me, and I was just watching the clock for them to finally end, and the jokes I found to be a mixed bag. In general, I enjoyed the gags involving animals, special mention to Steak, but the ones involving humans were more hit-and-miss for me, specially those related to Niche as they had a high chance of being ass jokes.

From this point onwards, expect SPOILERS.

Characters
I had a hard time sympathizing with the characters, a lot of them seemed to exist to fulfill some sort of role: Zazie was the lone wolf that learns to trust his friends, Jiggy the ultimate "cool" guy, LLoyd the "mysterious" guy, and so on…

Then you have characters like Thunderland who is introduced as some sort of monster that will stop a nothing to dissect animals just to then show he's a good guy, all in a way that felt like it was there to be just padding... him running with Steak made sense when he was what he was originally implied to be, not after the reveal he had been taking care of the cats rather than dissecting them and what not.

From the main cast, I'd say that my favorite is Connor, unpretentious and easy going, he just loves to eat.

For the letter bees in general, I'd say that Lily Confort. And I think the author did her dirty by snatching her heart instantly when you had pages upon pages to recover a heart when the plot called for it.

Setting
You'd think that something like having no actual sun would have a huge impact in the world, but what we know is that there are essentially 3 areas of different levels of riches based on how far they are from the sun, but it's not like any reason is giving for this. It's only like 15 volumes when we see many plants in the capital... but then we also see a giant forest outside the capital, so what gives?.

We also don't see goods being sent around, other than letters, it really doesn't seem like the capital sends food outside, yet, even though we see a few plants around plants, we don't really see crops around, it's a wonder how towns sustain themselves when even outside far off towns there's only fucking rocky terrains, rocky terrains everywhere.

I thought it would have other effects as well, with some places living in constant darkness, and others living in constant light, but I saw nothing of the sorts being seriously touched upon.

Story
As I mentioned, I wasn't really invested, and the fights just dragged the pacing down, specially when Reverse called the gaichuu, and it took multiple volumes to resolve, and even then, it's unclear what the fuck they were planning to do with that. So it eats the "man-made" sun which is actually a gaichuu... now you have another giant gaichuu and no sun, so what the fuck have you achieved?

And the closer it gets to the end, the more the manga drones and drones about information I couldn't care about, bogging down the pacing more and more.

The story was supposed to be about Lag searching his mom (which is eventually replaced with finding Gauche instead, and then the mother topic is dropped for most of the manga) and delivering letters, so I thought we would have more individual stories about the letters. But there are surprisingly few considering that this is 20 volumes long.

While I can't say I loved them, I still liked them more than the main plot in general. Something that got in the way was how people were often sinless victims or absolutely garbage with no redeeming qualities, with not much in between. And in the off-chance we got an ok story - like the working mother whose daughter died while she was out - there's a big chance there'll be obtrusive asses drawn and kind of focused by the shading and affecting the tone of the scene.

My favorite story was the one about the lighthouse

Nitpicks
Back when Reverse was leading the Gaichuu, Lag goes to help the human sacrifices but encounters Gauche and a verbal battle ensues before the actual fight, which ends with Lag getting really mad at him when he hears people got their heart taken. But while Gauche was placed there to hinder letter bees... at no point does Lag try to avoid him to go save the people, not only that, the one managing logistics and leading the people there was Roda, who was right there, but Lag is mad at Gauche specifically enough to say he'd kill him, while he grabs Roda who was falling to her death (which wasn't her death of course).

While Gauche is the one to take the Gaichuu of the ice, it's not clear how he achieved it when it's supposed that Maka doe shit that prevents people from entering, a thing that wasn't done when Lag came because he was with Niche.

There are several kinds of Gaichuu, and there are several of said kinds, yet somehow Zazie knew that X Gaichuu was the one who killed his parents? While a lot of Gaichuu live in specific areas, this one moved around which is why it took him years to find it, but that's even more of a reason to not know if it is the same one...

It's never explained why the majority of bees are teens or even early teens, you'd think adults would be better suited in general for this dangerous task, but there are very few of them that we actually saw.

While Lag got Sylvette's heart back, I don't think it was explained what happened to everyone else who had lost heart, because - if he could return hers - he should be able to return Gauche's, Lily's, Sunny's and more...right?

And in general, whether someone survived or died after losing heart seemed to be mostly on the whim of the mangaka.

You might also think you'd get fake mailmen too, or at least a cheaper, less curated, unofficial alternative considering it was said they were very expensive... but nope.

Conclusion
I wanted to be kinder to this manga - the premise is interesting and has a lot of potential, the art is good, and there's a big focus in a large cast of characters - but the execution doesn't work for me at all.

I didn't connect with most characters, making the individual stories underwhelming for the most part, and making the overarching story a chore to read rather than interesting. Sealed with the fact that I couldn't find anything to be excited about in the battles.

I also think that the way the author drew asses, crotches, and (sometimes) crotches, went against the kind of tone he probably wanted to set. Or at least it's my impression that it was supposed to be a sometimes heartwarming, sometimes bittersweet, story of putting your all to win against impossible odds and help your friends and all that jazz.

Looking back, the only thing I remember fondly is some gags, and that just isn't enough.