The Cannon Fodder Had No Choice but to Corrupt the Hero's Party

After transmigrating into a brave-hero game as a disposable Demon Lord's Army officer, he is immediately set up to die at the hands of the hero's party. A great archmage, reduced to swinging his staff in hand-to-hand combat, is beaten to death by the entire party.

But that's fine. If he can't beat the hero's party, then he'll join them (crossed out).

Of course, he'll corrupt them all and turn them into his own people. If he can't beat them, he can make them join his side. The mage, the saintess, the hero, one by one, all in a row. The big-sister mage turns into a vampire. Wait, why aren't you sucking blood? The pure-hearted saintess turns into a succubus. And you, the hero... What do you mean you've turned into the Demon Lord?