Arc Fatigue: Inverted. As put in pretty much every review, one of the main flaws of Kabaneri was how rushed and compressed felt its story due to the short length of the series, which was also noted to have prevented the makers from exploring the setting despite all the work that had been obviously put in creating and elaborating it. Some of them even commented it looked like the producers had tried to fit an originally 24 episode series in half of that length.
Catharsis Factor: Ikoma on a rampage in the first season finale and delivering a pitiless and raw execution to the scientist responsible for a little brother's death.
Conflict Ball: After settling their differences in the series proper, Mumei and Ikoma pass this around in Unato Kessen. Ikoma refuses to talk to her and snaps at her when the nobles refuse his plan, and she attempts to fight everything by herself and nearly gets killed. While the movie ends with them reconciling their differences and trusting each other (and explained away as being part of Unato's Hate Plague), a lot of fans think that their relationship took a big step backwards for no real reason, since by the end of the first season they had learned to trust each other.
Kurusu's gotten a lot of love in terms of supporting characters, due to his solid design, his skills in battle and being a competent Only Sane Man.
Fandom Rivalry: With Attack on Titan for obvious reasons, but it escalated big time when AoT's 2nd season was revealed to only be 12 episodes long (keep in mind fans have been waiting for an S2 for four years). AoT fans have blamed Kabaneri for this as Wit Studio already announced a 2nd season of Kabaneri was due in 2018, and are rather bitter that a supposed "inferior Titan clone" is getting a second season far faster than the "original" series did. Fortunately the hate train died down a bit when Titan's third season was announced to be released on 2018 too. It eventually turned out that there was no second season at all: the Kabaneri project scheduled for 2018 turned out to be a mobile game, followed up by the 3-episode mini-series The Battle of Unato which released in May 2019.
Genius Bonus: Being set in an Alternate History post-Industrial Revolution Japan, there are elements of the show's society that make a lot more sense if you're familiar with Japanese history:
The bushi being massive jerks to commoners is Truth in Television. Samurai in reality were a privileged class, and all too often they took advantage of their social status to abuse their lessers. An excellent example of this is the bushi in Episode 7 who demands the gunsmith repair his musket first even though Ikoma was already there before him and then gets furiously violent when Ikoma tells him to wait his turn.
Not explicitly stated, but this show demonstrates a rare literal case of Fantasy Gun Control. The only characters in the show who use guns are the bushi and the Hunters. And even then, there are degrees of gun control in Kabaneri: your average bushi has a simple steam musket, but the Hunters have far better equipment, such as Mumei's dual sawed off shotguns and the Kokujou's mortars and attack motorcycles. Japan has a very long history of weapon control, ranging from sword confiscation laws in the Sengoku Jidai era to similar laws today, which include some of the strictest gun control laws in the world.
Hilarious in Hindsight: Takumi is Ikoma's good friend and voice of reason. So it's pretty funny with all the comparison to Attack on Titan to find out he shares Eren's voice actor. Even more hilarious with the release of Fire Emblem Fates, which also features a character named Takumi voiced by Yuuki Kaji who lives in a fantasy version of feudal Japan.
Auto-Erotic Asphyxiation!Explanation Ikoma's means of overcoming a bite involves cutting off the blood flow to his brain by strangling himself using a special machine he made.
"Ikoma is a masochist" jokes are quite common.
Peasant-chan! Explanation Due to the Kumamoto earthquake on April 14, 2016, the originally scheduled broadcast of Episode 2 was delayed a week. However, a Chinese streaming service had already started airing the episode before the order to delay came through and viewers saved and distributed a copy of the episode after the embargo went into effect. The episode was fansubbed with dubious quality including this hilariously bad aforementioned line when a man gets devoured by a pack of Kabane (the line in question in reality is the man's name, "Momoya"). Other issues include two situations where Ikoma's combat against the Kabane are censored, and an egregious delay in the audio track.
Also, "2.8 (IDK what Measurement)" Explanation Also from the above, the fansubbers for Episode 2 clearly didn't know that Mumei was speaking of the "ri" unit of measurement that was in common use in feudal Japan. The official Amazon subs translated it as 8.7 km, which 2.8 ri might be equivalent to. The ri measurement has had many different values throughout history.
Habaneros Explanation People like to refer to the Kabaneri or Kabane as habaneros sometimes, because they sound similar and habaneros doesn't get picked up by spellcheck or autocorrect. The whole title is sometimes played with this way, leading to things like "Habañero of the Spicy Fortress".note The other reason is Mumei's pose when she cuddled under her cloak to sleep in the Episode 2, which did make her look like a habanero.
KISAMA Explanation The short pre-opening sequence in which Ikoma is asked "貴様、人かカバネか？/"Kisama, hito ka Kabane ka?"/"Are you human or Kabane?" drew a lot of attention for the copious amounts of Narm it contains. This resulted in lines from the sequence being frequently posted in discussion threads about the series.
HARD CHICKEN and HARD FREEDOM Explanation Comes from Suzuki's Gratuitous English in the episode previews. One had him say "hard," "freedom" and "chicken." "Chicken" especially became popular in Japan, largely because of Japanese fans who weren't familiar with the phrase.
Moral Event Horizon: Biba crosses it in episode 9 by siccing the Kabane on an entire town because of the lord's perceived betrayal years ago.
Then he ups himself in episode 10 by killing Takumi in front of Ikoma (he performed a Taking the Bullet however) and taunting the latter over it, and brainwashing Mumei and having her stab Ikoma and kick him off the Kotesujyo into the ravine.
In episode 2, a Kabane damages the train's boiler by slamming against it, but dies in the process; what makes this ridiculous is that it does so by spinning through the air screaming, and then hitting the boiler so hard that it (the kabane) explodes. It almost borders on slapstick.
The Hunters make their debut in episode 8... and ride into battle by jumping motorbikes out of their train. There's no foreshadowing anything of the sort existed (motorcycles are unheard of in most Steampunk settings), and plenty of viewers had to do a double take at it.
Biba's name. While it is worse in some languages than in others, in most of them it sounds like baby babbling.
Ikoma's loudly screaming reaction to Takumi's death. Aside from that, it makes it look like Ikoma expected their revolt to success without a single casualty in their side.
Biba's seen as the worst part of the show. Many people consider him to be a shallow Card-Carrying Villain whose actions were often illogical or overly extreme. Tons of people, even fans of the plot shift and the story he brought, remained confused as to what he was even trying to do half the time. His only redeeming factor is the fact that he is voiced by the fan-favorite Mamoru Miyano. And of course, Roger Craig Smith in the English dub.
Kageyuki is also viewed as a lame villain with a generic backstory. It doesn't help that he only gets a few minutes to fight and is unceremoniously killed off so the Final Battle of Unato Kessen can be against yet another Black Fog.
Strawman Has a Point: The nobles in Unato Kessen are meant to look like idiotic Obstructive Bureaucrats when they refuse to allow Ikoma to carry out his plan. The problem is, his hypothesis about the Kabane's behavior is based solely off speculation and he can't deliver any proof when the nobles press him about it, and he doesn't help it by getting visibly angry when they refuse his plan. While Ikoma is 100% correct, the nobles are treated as classist Jerkasses for not accepting on blind faith that he is right.