Note: this review contains major spoilers for the Kabaneri of the Iron Fortress TV series.

Kabaneri of the Iron Fortress: The Battle of Unato is the theatrical sequel to 2016's 12-episode TV anime, Kabaneri of the Iron Fortress. The series ended on a cliffhanger of sorts; while our heroes managed to escape with their lives, the capital was destroyed and the Shogun killed, leaving the country leaderless. The Battle of Unato therefore has the important task of setting up the new status quo for the franchise going forward.

Picking up six months after the end of the series, The Battle of Unato follows our heroes as they make their way back to where they started—hoping to retake their town and make it into a paradise similar to old Japan before the kabane came. However, getting back has proven to be no simple task. The problem is that the rail lines connecting the northern half of the country to the southern half have become inaccessible. With the collapse of the central government, each station has become a country unto itself, leaving each to be controlled by one warlord or another. Luckily for our heroes, their armored train makes them a powerful group in their own right, and so they are able to enter into an uneasy alliance with three other factions to take back a previously lost station. When this task is completed, they will have cleared a passage south towards home.

From the start, it's easy to see that the world has changed drastically. With no Shogun, humanity is no longer united against the kabane, instead splitting into factions based around specific ideals. On the other hand, these newly minted groups are willing to risk both manpower and material to take territory back from the zombie hordes—something the old government was loathe to do. However, this doesn't mean that everyone gets along. While each group in the film is committed to taking back Unato station, each has their own set of reasons for doing so. What makes the situation even more tense is that, through the participation of the Koutetsujou and her crew, people are learning about kabaneri for the first time, and their reaction is far from positive. Much like the Koutetsujou crew in the early part of the TV series, many see little difference between kabaneri and kabane, treating them like ticking time bombs at best and traitors to humanity at worst.

At the center of this powder keg are Mumei and Ikoma. In the time since the end of the series, the two have become a powerful and cohesive unit. While she takes the lead with her speed and agility, he has become the shield she always wished him to be. And while he's made no inroads on turning them both human again as he promised, the Koutetsujou is already carrying a supply of rice plants to transplant when they return home. Ikoma's promise to her has become the center of Mumei's world after the betrayal and death of her brother. It is the guiding light that has replaced her brother's principles in her heart. Because of this, Mumei has grown closer to the Koutetsujou crew. While still stoic and no-nonsense in battle, she's even willing to partake in some girl talk with Kajika in her daily life. Of course, it's no surprise that the person she's become closest to is Ikoma, and for the first time in her life, she finds herself harboring romantic feelings.

Unfortunately, this revelation couldn't come at a worse time. Something is very wrong with the area surrounding Unato. Both Ikoma and Mumei are quick to tire when using their kabaneri abilities and are having trouble controlling their emotions. Ikoma in particular is becoming more and more emotionally unstable—to the point where he appears to be more kabane than kabaneri at times. And to make things worse, the kabane around Unato are moving in odd ways, suggesting an intelligence behind the horde, something the coalition forces initially dismiss as madness.

On the other side of things is the film's villain. While he gets little screen time—perhaps only five minutes or less total—he's still effective as a dark reflection of our heroic duo. In many works of fiction, there are “arc words”—a set of words repeated throughout the series that thematically connect the characters to the story. In Kabaneri of the Iron Fortress, this is the question “What are you (human or kabane)?” It is the central internal conflict of the story in which Ikoma struggles with understanding what he has become and what that means for his identity as a person.

In the second episode of the TV series, Ikoma reached his lowest point. After being shunned by the survivors of the Koutetsujou and cast out, Ikoma nonetheless saved the train. However, when his friend Takumi tried to rescue him over the objections of the crew, Ikoma ignored the gesture. In his despair, he has asked the question and accepted the answer given by those on the train: he is a kabane. However, then Mumei appeared before him and told him the truth. He is neither man nor monster: he is a kabaneri. From then on, he is asked “What are you?” countless times. Eventually, the question grounds him during his greatest trial and gives him the strength to maintain control because it forces him to answer: he is a kabaneri.

With the villain of the film, we see what happens if a kabaneri answers this question and things don't go nearly as well. When he asks his friends what he is, none say “human” nor do they simply call him by his name. Instead, they react with fear and bloodshed, leading him to conclude once and for all that he is kabane, not man. In other words, he is what Mumei or Ikoma could have become without various people supporting them and believing in them. He is their dark mirror. And as we learn, a kabaneri who chooses the side of the kabane is potentially more dangerous than any other threat.

On the visual side, the anime looks great. As with the TV anime, the film reaches a new level of beauty in its closeup shots, filled with detail and dynamic color. But what really stands out are the action scenes. This film gives Mumei a new weapon: a steampunk Winchester with an anti-kabane bayonet on the front. Each battle she fights is basically a mixture of shooting, martial arts, and color guard theatrics. It's a spectacle that's a ton of fun to watch. The music is likewise excellent. From the mind of composer Hiroyuki Sawano (Kill la Kill, Attack on Titan, Re:Creators) comes an expansion to his score on the TV series that brings back some old favorites and remixes others into something new. And then there's the credits. Stick around for the credits.

When thinking about Kabaneri of the Iron Fortress: The Battle of Unato, I find myself returning to the same question: “Is this a story that had to be told on the big screen?” The answer is no, and if anything, the stakes are lower than they were in the TV series, as is the danger posed to our heroes. However, that doesn't mean that it's a throwaway film with no lasting impact on the overall story, like many an anime film based on a TV series. The Battle of Unato does a ton of heavy lifting. It sets a new status quo for the story while delivering a thematically relevant narrative. Moreover, it continues the development of our heroes after the climax of the TV series, with a lot of focus on the evolving relationship between Ikoma and Mumei. Simply put, it's a vital part of the main story with enough awesome action to keep you entertained throughout.