It's quite good, but I have a niggle about its politics.
I'll start with the good stuff. It's set in a steampunk universe where there was a Wind Revolution ten years ago and the king and queen got guillotined. The Ballesteros Empire is now a republic, but they're not the only geopolitical game in town since there's also a Holy Levamme Empire and possibly also the semi-mythical Sky Clan. You'll have noticed lots of words related with flying, sky, etc. This show's heart is in the air. Everyone flies. As the show begins, our heroes are about to go off to train to become pilots on the flying island of Isla and (hopefully) find the End of the Sky.
The early episodes include light-hearted school stuff, e.g. a swimsuit episode and everyone running a ramen stand at a school festival. Occasionally it's a bit silly, as with the cooking failures in ep.6 or the "fall on top of her" cliche in ep.5, although in fairness the latter turns out to be a crucial element of the episode's story. She's messed up about their identities and it affects her piloting in the mock battle. Later on, though, we get dogfights and death. The Ballesteros commanders are willing to send their students into battle against the enemy, even if it's a suicide mission to buy time for their main forces. Named characters can die.
Meanwhile the cast have issues. Some were personally involved in the Wind Revolution. Your mother's decapitation isn't something you'd forget in a hurry. Themes being addressed include duty, forgiveness and self-sacrifice. These aren't the most vivid characters I've ever seen, but they're sincere and thoughtful in how they approach their lives and deaths. They're aware of their responsibilities. They can also be funny, e.g. our hero's relationship with his sister. I liked them.
I have no reservations at all about the setting and worldbuilding. I like its scale. I like the aesthetic, with all that lovely flying. Miyazaki would approve. Does 1920s count as steampunk? Well, who cares? It looks pretty, anyway.
Unfortunately the show also feels, to me, right-wing and reactionary in a way that approaches sexism. That's "right-wing" in a Japanese sense, of course, i.e. nationalist and at worst history-revisionist regarding World War Two. (I've mentioned before that capitalism vs. socialism is a debate that doesn't exist in Japan... by British definitions, the entire country is right-wing.)
This show's heroes will become pilots going into battle. Theoretically they're equal-opportunities, with as many girls as boys (and gender-neutral pilot suits), but in practice it's only the manly men who get killed or go heroically off on a patriotic suicide mission for their country. (They're not kamikaze pilots, but they're still not expecting to come back.) Death is noble. Death is honourable. Death is expected for a true warrior. "We all have amazing power sleeping inside us." Of course your woman will mourn your demise, possibly as she's forced to give up flying and become ground support staff (e.g. an engineer). Meanwhile the only big self-sacrifice performed by a female character in this show is a passive one, in which she lets herself get handed over like a trophy or an object.
What's more, the show's portrayal of war is... fuzzy. Battle is joined against the Holy Levamme Empire because, um, they're in the air too. They see them and attack. Did anyone try talking? Unless I've overlooked something, I don't think anyone even suggests that there might have been a reason for opening fire. This is underlined afterwards when the two sides' officers have a chin-wag and casually agree to work together. What had been the point of fighting in the first place, then? In other words, war is like weather. It just happens, like the sun coming out. We shouldn't be asking who started it and why (ahem, Japanese invasion of China in the 1930s). This is then taken to another level with the Sky Clan, whose reason for fighting is "God told me to". Almost all high-level decisions taken by any country in this show are taken on the basis of national religion.
Apart from anything else, this undermines the drama. The battles in the second half lack weight, since they're happening for no visible reason. A faceless enemy attacking Isla isn't actually that interesting. Frankly, even the deaths of major characters are thus arguably less strong than they might have been, although the survivors' grief afterwards is powerful.
Then we have what happens in ep.13. The show's hero declares that he's going to "reopen negotiations" and take back by force something of no material value that was handed over fair and square. By "negotiation", he means "declare war". I don't think he even attempted a diplomatic solution. (Besides, if he really cared so much about [SPOILER], couldn't he have gone over himself as well in ep.12?) I spy a metaphor for childishness over disputed pebbles in the South China Sea.
On the other hand, though, learning how to forgive, not hate, is a key element in this show. Its view of soldiering is also more nuanced than the above analysis would suggest, with important characters quitting the military at the end and the loss of friends being a source of deep and genuine pain. It's a humanist show. It cares about its characters and it tells their stories honestly, with their loves, hatreds and conflicts.
Observation #1: in ep.11, surely he can't hear her? He's flying around up there in a plane! Her words wouldn't have got through had there been twenty of her, with megaphones.
Observation #2: the hero is called Kal-El (i.e. Superman). What?
There's a 2011 film set in the same universe, incidentally, called The Princess and the Pilot
, but apparently there's almost no overlap between them. Also the film was made first, but takes place afterwards. They're all based on novels by an author called Koroku Inumura.
Despite my negativity, this is a delicate and even charming series. It has quite a sweet love story, at least until a certain person becomes a warmonger in ep.13. I enjoy its aesthetic and the delight it takes in flying. I don't even mind the open-ended finale, which suggests that they're hoping to make a second season but could also be read as leaving open the possibility that our heroes drown the world in blood before being executed for war crimes. I'm like that. I'm a big softie when it comes to hoping for happy endings. (I'm being semi-flippant, yes, but that's still 50% serious.)
Above all, though, the character stuff works. The cast carry the show and that's the most important thing. The relationship between Kal-El and Ari I like, with their sickbed conversation in ep.8 being easily the best thing in the episode and far more appealing for me than the earlier dogfights. This show will make you cheer when someone kicks down a door and punches our hero in the stomach, but not in a malicious way. He'd been in a bad place. He'd needed that. If there were another series of this, I'd watch it.