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The moment we faced the Demon Army, I was able to instantly tell how many Demon Lords there were out there. I quickly detected three of them. Each one was standing at a cardinal direction, for some reason.
And all three of them exuded a similar amount of Demonic Energy than the one that tried to kill Monica back then. Most likely, these bastards were directly serving another Archdemon.
It is most likely possible that the Demon Overlord that took over Silvertide's Capital is serving the Archdemons, and these three are his servants.
If that's the case, the best way to deal with them right away was to just divide and conquer. While our armies took down the sheer, ridiculous amounts of demons, we would quickly go for the behead the general tactic.
Kill the three Demon Overlords overseeing the entire battle and then destabilize the rest of the army. Once they notice their leaders are dead, they will have a really hard time adapting to the situations as easily.
Check "The Protagnist's Sister Is Actually the Strongest"!