Mahou Shoujo o Mechakucha ni Shite Mita ~Houkai Akuda~

The protagonist is an evil monster, Black Ripper. He had slipped into the heart of his enemy, the justice forces commander, when he was shocked by a blast. Thereupon, using the commander, he is trying to lead the organization of justice to ruin, making magical girls plunge into evil. To turn it to evil, he ought to make magical girls despair. Moreso, the more magical girls despair, the stronger they become. Wouldn't it be a great shock if their commander betrayed them? The girls believe him from the bottom of their hearts. In addition, they are not thinking about him just as a commander. They seem to have deeper feelings for him. If so, it would be beneficial to let them enter into relationships they desire. The protagonist thinks of getting involved with them deeper and then betraying them. A respected mentor in combat, a trusted superior of the base, and the dearest lover. He needs to become an irreplaceable being to magical girls. And, becoming the most important person to the girls, he splendidly betrays them before their own eyes. And when they know that they were betrayed, grief will overcome them. The grief will lead to the birth of the most powerful dark magical girls. Will the protagonist succeed in enslaving both the bodies and minds of girls, as he expects? [Translated from DLsite]