Acting for Two: Zanki and movie-only Touki. Lampshaded in the after-credits movie teasers.
Anti-Villain: Kabuki turned on the Oni and the villagers because he was sick and tired of being called a monster, even when saving their lives.
Arbitrary Headcount Limit: A non-game example which is mixed with Foregone Conclusion. If you've been counting the Oni that have been gathered, you'd notice that there's eight. Sure enough, that eighth Oni pulled a Face–Heel Turn and was killed before the climatic battle with the Seven War Oni.
For Kabuki in The Movie. At first, he seems to be the kind of guy who would be the perfect fit for what Past!Asumu needs to fight off the Makamou, but after he's done fighting one of them in his first appearance, he asks the villagers for a reward and is pissed when he's given dried sweet potatoes, but was willing to give it to a kid... had his mom not thrown it away and told him an oni touched it.
In the same movie, the other Onis get their ECMs as well. Past!Ibuki gives up his life as a Daimaou because he finds it boring, Touki shows off his Buddha mind powers, Kirameki flies in via hang-glider and realizes that he was too late to join the battle with the Oni, Nishiki during his execution catches a blade with his teeth and like Kabuki, required money for his job (though he joined through the faked promise of buried treasure), and Habataki was retired until his wife talks him into helping the Oni out.
Fantastic Racism: Happens a lot in the movie, with a lot of prejudice towards Oni. It actually becomes the motivation for the villainous Oni, Kabuki.
For one, Hibiki isn't the one who gathers the group, but rather Asumu and Kabuki, the latter being far from an actual hero, but Hibiki had the makings of The Lancer in that formula (Kabuki knew where he lived and went to him first).
While the villagers are unable to fend for themselves, they also refuse the Oni's help due to Fantastic Racism.
The team actually fails their first fight.
No such training ensues.
A combination of the villain threats, villagers' wariness, and one of their own manipulating them to fight each other resulted in the team to split.
The next few plot points happen according to form though (save for the villagers joining in the battle, but to be fair, they're muggles facing against a group of monsters that intend on feeding an Eldritch Abomination), though with only one death on the Oni side that, in retrospect, was not part of the titular Seven War Oni despite forming them.
Non-Serial Movie: Despite providing a backstory for the Takeshi organisation, the different origin for the Armed Saber and the actual presence of Orochi, an offscreen monster in the series finale, qualify The Movie under this.
Ungrateful Bastard: The villagers in the Hibiki movie. No matter how many times the Onis save them, they play the Fantastic Racism card on them. Is it any wonder that one of the Oni got tired of their shit, killed some of them, and teamed up with the villains?