Totsuzen Kaijin Ken Jimuin no Ore ga Mahou Shoujo-tachi o Otosu Hanashi ~Mahou Tenshi Angel Saber VS Aku no Soshiki Death Brand~

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

And it's member, Tachikawa Masashi, has been fulfilling the duty of non-combatant grunt.

Until one day, when executive Ragulia transforms him into a monster. Why was that? There were the following reasons: cost reduction (lack of budget) and the makings of a monster. Masashi hated that, but he was threatened that if he refused, he would be fired and wouldn't be able to return to human form, and he was forcefully put to work. He was appointed to fight magical girls.

(This was a summary of the first title of the trilogy).

...Several months later.
Masashi has completely settled as a monster and a clerk at the same time. Usually he did office work, but, in the event of something happening, he worked as a (backup) monster. One day, he and Ragulia were called by the branch office chief and were announced that they were assigned to the new duty (with transfer): "to revive a branch in one provincial town".

...Nevertheless.
Two of them, who took up new posts, were at a loss for words from shock. That branch had many problems; it wasn't even operating. Equipment wasn't ready, combatants' skills were low, there weren't any monsters... These conditions were so extremely grave, so the "self-proclaimed" organization of justice, Justia, said that they would willfully destroy themselves and left them alone. At first, Masashi and Ragulia despaired, but in an attempt to some way or another recover the situation, they whipped their weakening hearts back into form and began to work constructively.

...And yet.
Justia sensed these movements, misunderstood something, and suddenly sent magical girls. Moreover, Death Brand's upper brass dispatched a female inspector in order to evaluate Ragulia. Masashi has to rectify just the worst situation ever, but in order to do it he ought to fight magical girls and even get involved in the organization's fractions and struggle with them.

Each one's thoughts are mixing. Each person's sense of values will soon be called into question. What is actually justice? What is evil?

...And so.
"I was sent here because, due to the state of the budget, a guy who can work as a monster and a clerk is only needed, wasn't I?... No, I've already given up on that, so let me work as normal."

Will Masashi be able to return to peace and quiet?