The first thing to speak of about this series is that the title and blurb are misleading, it's a really generic power fantasy harem isekai with some comedy, the mastermind and organization stuff are ultimately just a gimmick and mostly irrelevant.
First the story:
A guy wants to be a mastermind in the shadow -> trains a lot -> realized it's not possible on earth -> is reborn in another world with magic -> create an organization to fight off the cult of Diablo (a completely made up enemy).
The start is actually quite good, the MC training and death on earth making for a fun parody of the usual isekai tropes, and his infancy and childhood in the new world serving as a nice introduction to the story.
It's after that that things start to go south, first there's too much time skips: the whole creation of the organization is skipped, we also don't see how the MC deal with his lies. Which if, like me, you've started reading expecting a story about a mastermind controlling both sides... Is rather disappointing.
But at least the story is rather quick to show it's true colors, and we rapidly see that: the organization doesn't matter it runs itself, every lies of the MC just turn out to be true so he doesn't have to deal with it, and the actual goal of that series is just to follows the double life of the MC.
That life consisting of 2 sides: his public identity where he tried (and fail) to appear as a normal student and Shadow the cool op and (above all else) edgy anti-hero fighting a cult.
After that there's no real story we just follow the MC while both his organization and the cult act out, nothing particularly interesting and overall quite predictable.
3/10
Characters:
It's hard to judge the characters mostly because most are so irrelevant, but the few that are developed have some interesting interaction so it's not that bad.
First the MC: he is the best character and by far, unlike most protagonists from similar stories he is quite apathetic towards others and doesn't shy away from being amoral if need, sadly he is also a dense moron.
Overall he is quite fun to follow around and his focus on acting cool or like a normy (depending on his identity) makes for some good comedy.
Sadly the other characters are barely worth mentioning, most have a name, a function, and some basic personality trait and that's it, even the girls appearing on the cover and color images are mostly just plot devices. And when they get some development it's usually just for that arc and they go back to being irrelevant after that
Also don't expect other male characters to be important, they're all either background characters, enemies or pathetic tag along whose function is to make the MC look good.
That said none of the characters are annoying and the interactions are for the most part pretty well written.
5/10
Worldbuilding:
To put it simply there's none, be it geography, politic, or magic we only know the bare minimum for the story to kind of make sense.
1/10
Art:
8/10 Really good, the girls' design is especially good. But it's a novel so it doesn't really matter.
All that said despite all the negative it's overall not that bad as the writing is good and the story flows well never being particularly good but also never really annoying. Surprisingly there few true comedic moments, but the few there is are good.
5/10
To conclude if you like that kind of cliché power fantasy it's can be an enjoyable, if predictable, read.
If you would rather read something closer to what's described in the blurb give a try to "There Was No Secret Evil-Fighting Organization (srsly?!), So I Made One MYSELF!".
