Slop.

Honestly, in-story context isn't even needed. Genocide is always wrong. But with the in story context, people trying to justify the fictional genocide is even worse because there is absolutely nothing in story that suggests that a genocide was even remotely a justifiable thing.

I could not give you a more clear cut example of a black and white fictional genocide. This is a story where the "sword master" (villain of the story) is revealed to have murdered 200,000 civilians after their government surrenders in a war. Why? Because as he says, "the children of that nation grew up being taught its destructive ideology" (wouldn't be surprised if the author intended this line as a dig towards isr*el).

Even any excuses of that nation being a military threat are completely moot, since

1. The military strength of that nation relies on a resource called "datenseki" ("spirit stone" in english) which Japan steals after the genocide.
2. The "sword master" killing all these people single handedly using his magic nuke proves which country was the actual military threat.

Point 1 also completely calls into question the Japanese government's narrative that they were defending themselves from agreessors who appeared suddenly and attacked without reason (even more isr*el parallels).