突然怪人にされた俺と悪堕ちする魔法少女の話（Totsuzen Kaijin ni Sareta Ore to Akuochi Suru Mahou Shoujo no Hanashi）

There is an organization, Death Brand, plotting to conquer the world.

And there is an organization of justice, Justia, which is trying to obstruct the plan.

These two organizations signed a "War Pact" promising to wage war while adhering to the rule — "Do not involve ordinary people in fight" — and they did so, fighting day after day.

However, one day during the war, unrelated students Tsujitani Takashi and Minakura Kumi were abducted by one of Death Brand's divisions—Death Heat.To break Death Heat's present inferiority, they put into use a despicable strategy ignoring the War Pact: they subjected ordinary citizens to a remodeling surgery and turned them into military assets.

Luckily for these two, they were saved by Justia's magical girl, Iren, yet it was too late and they were already remodeled: Takashi into a monster and Kumi into a magical girl. They asked for help to turn them back to humen, but were told that in order to do so, there was no method but to complain to Death Brand, get them to admit that they were at fault, and undergo restoration surgery. Furthermore, Iren was their classmate, Akazuki Ayane, and she too was taken away and remodeled, as she explained.

Death Brand performs an internal inspection and needs about two weeks to capture the fact of Death Heat's violation of the Pact. Death Heat, on the other hand, desperately tries to intervene, even attempting to have the two undergo brainwashing surgery.

"We will never... ever forgive them!"

In order to defend themselves and for the tragedy not to repeat itself, two of them decide to fight. Will they actually be able to return to human form?

[Translated from DLsite]