The following contains spoilers for Episode 9 of Overlord IV, "Countdown to Extinction," now streaming on Crunchyroll.
There have not been many times when Ainz Ooal Gown's emotions have gotten the better of him. Since being trapped in his lich lord form in the former video game Yggdrassil, he has somehow managed to simultaneously lose his humanity, and come to operate by it. The pending plan devised by his most conniving Floor Guardians, unofficially codenamed "Carrot and Stick on the International Level", has seen the decimation of several human villages around the Kingdom of Re-Estize on Ainz's order.
While the impending war against Re-Estize was caused by the foolish actions of a self-interested noble, the pattern of self-interested, foolish actions in the human factions of Yggdrassil has been a constant theme in Overlord IV; however even an assault on Sorcerer Kingdom goods in transit and the subsequent declaration of war on Re-Estize aren't indicative that Ainz's actions are personal. Overlord IV episode 10 is different. The foolishness of the humans and the elites of Re-Estize has brought on something we don't see often: the fury of Ainz Ooal Gown.
The Call is Coming From Inside the Palace
The episode begins in Nazarick, with Ainz and the Floor Guardians discussing the emergence of the adamantite-level adventurer, as well as the plan to take down the royal capital. The episode continues in similar fashion to the one before it – in the throne room of the king-to-be, Re-Estize's Prince Zanac. He is deep in conversation with his younger sister, Renner, who is his important advisor. They discuss possible ways out of the conflict, as well as the status of their now-detained father, who is being kept in prison for his health and safety, but also due to his opposition of the plan to engage the Sorcerer Kingdom in war.
King Ramposa III wishes to cut their losses; however, Zanac is aware of the fact that the Sorcerer Kingdom has slowly been advancing north, through the territory of Marquis Raeven, but he wonders how they did it so quietly. Renner brings his attention to the fact that the only person capable of keeping a secret of this nature would be Marquis Raeven, possibly threatened with the harm and death of his son if he does not comply. The Sorcerer Kingdom's path has been such that aid cannot travel through Raeven's domain to offer aid to Re-Estize, effectively a strategy that seeks to box Re-Estize in before the war even starts. Knowing that royalty is needed on the battlefield, Zanac prepares to don heavy armour and lead his forces.
Adventurers Join Forces?
Elsewhere, the adamantite-level adventurers of the all-female Blue Rose faction meet up with Lakyus's sleazy uncle, the leader of the only other adamantite-level faction of Re-Estize, the Drop of Red. Their meeting is intercepted by forces from the secret unit of the Slane Theocracy, in hopes of banding together against a common threat: the Sorcerer Kingdom.
The stakes are high, as these factions that tend to butt heads attempt to coalesce, but their differences prove too great. Each faction resolves to deal with the Sorcerer King's arrival somehow before going their separate ways.
The Eve of War
The army of Re-Estize watches cautiously as they assume their positions. The acting King Zanac arrives on the battlefield and asks for an audience with Ainz, alone. When Albedo delivers news of the solitary King Zanac hoping to speak to him, he offers to go by himself on the basis that Zanac also came alone. Ainz sets up a long table and some glasses of water for them to drink as Zanac asks him what he wishes to know. Throughout the conversation, Zanac comes to realize what Ainz's true goal is: the attainment of happiness for himself and his dearest people. Zanac, being human, understands the goal all too well, and while it is regrettable that the path to this happiness will see the death of countless people; not to mention the destruction of the Kingdom of Re-Estize, Zanac feels something he never would have expected: the sensation that he and the fearsome King of the Sorcerer Kingdom are actually kindred spirits.
Ainz never gets the chance to express his budding feelings of admiration for Zanac, whom he sees as a true example of what interactions with actual royals should feel like, and with the way he expresses the thought, it's clear that Ainz still finds himself and his leadership lacking. While Zanac's desire to meet Ainz was inspired by his desire to have the Sorcerer King rethink his desire to go to war, he leaves the conversation feeling somewhat satisfied with the impasse at which they arrive. Put simply, Ainz and his people cannot achieve happiness without the sacrifice of Re-Estize, and Zanac has come to fully respect that about him; however, the nobles of Re-Estize, and even some of the forces themselves feel the need to save themselves, rather than face their destruction head-on as the Zanac does.
Head of State
Since Zanac is serious about engaging the Sorcerer Kingdom, some nobles feel that his time in office has come to a close, and they quickly turn on him. Knowing that there is no way to avoid war, they decide to attempt to placate the opposing force with something that had already been offered and declined: the head of the king. Zanac, having come to understand his counterpart a little better, is betrayed and murdered by some self-interested parties, who foolishly present his head to Ainz.
They beg for asylum for themselves and their families, but what they don't understand is that Ainz's quick acceptance of their terms is a simple ruse. Underneath the unwavering voice and demeanour, deep in the soul of a lich lord who had just made a new friend, something had stirred, spawning something we don't see every day: the fury of Ainz Ooal Gown. Ainz quietly orders his minions to ensure the suffering of all the parties involved, asking Aura that the humans who betrayed Zanac be made to suffer immensely for what they've done. The imminent end of Re-Estize has only been hastened, and this time, it's because the foolish actions of nobles have made this war personal.