10 years in captivity, zero years in planning: the reality of Adonis' 'rampage' looks just a bit silly in The Kingdoms of Ruin.
It is claimed that having spent ten years in captivity, Adonis would know how to most effectively destroy the civilization he hates so much. But would he?
The Kingdoms of Ruin (Hametsu no Ōkoku) is at this point a revenge story. It started with the humiliating execution of the witch Chloe, who Adonis was an apprentice to. He was forced to witness her death, and then, he was imprisoned. A witch saved him from imprisonment but was shot right in front of his eyes when he had almost been convinced to stop his rampage.
In other words, female leads have been killed twice in front of the male lead, Adonis, which renders him very angry and ready to destroy civilizations. In addition, the narration suggests that Adonis is well-prepared for that task, in particular, because he had spent ten years in captivity, thinking of the best ways to end the human race.
However, when Adonis is free to do his magic and destroy humans, he does not seem to have a plan.
A Tale of Chaos, Not Strategy
There is little rhyme or reason to his actions, even though they are, admittedly, quite destructive. One of them, for example, is to ride a huge golem toward the Emperor's property. The golem causes a lot of destruction, but it does not seem to touch the Emperor, who, it can be assumed, Adonis wants to kill for what the old man had done to Chloe. However, Adonis is not too hasty in getting there.
He spent 10 years figuring out the best way to destroy a nation"
The way: "lol, just walk towards the palace on a giant" (via u/Florac on Reddit)
Here, one can argue with the narration.
The witchery of Adonis is not the most effective method of ending humans; there is barely even a method. And Adonis himself does not seem to be very good at figuring out what he wants. He does not even try to get to the Emperor as soon as possible; at this point, it seems that the only thing he wants is to rampage, and even that is not very helpful because, according to Adonis himself, he does not get happier from all the terror he is causing.
It is here that we might note that solitary confinement is not known for improving human's ability to have revenge. In fact, if we assume that Adonis had spent ten years in solitary confinement, it is very unlikely that he has gotten anything but a major trauma from such treatment.
Even if he had spent ten years thinking about his revenge. As a result, what the anime shows is different from what the narration implies, and Adonis does not seem to really have a plan.