First, every character is a mary sue. Every last one of them. Tatsuya, only being the sueiest of them all, should always have "he's also a ninja" appended to any description of him. Tatsuya is a super genius and secretly the master technician taurus silver, known the world over for his creations. He's also a ninja. Tatsuya is a magical super soldier with the powers of a god. He's also a ninja. Hell, they even have a kiss to unseal power trope going on. Why such a seal even exists is beyond me as all it apparently does is seal god level power down to just demigod levels.

Basically, the author's character creation process is thinking something is cool and throwing that on top of a character.

Second, every woman is beautiful, yet I have no idea what any of them actually look like. Seriously, there are no descriptions of physical characteristics past the first intro blurb. With one exception (because it's apparently relevant to her character/powers), you will never even be told what a character's hair color is. All that is left is completely nondescript descriptions of women's beauty that, had the author been sixteen, would have rankings of them based on how bangable they are. You will suffer elaborate info dumps about fashion however, which essentially regresses over a century so exposed ankles basically equates to slutdom.

Third, it's all exposition. The author is pretty much only interested in info dumping the psychobabble of a magic system. There is nothing that can go unexplained and frequently goes explained far before it's even relevant. If you don't like spoilers you might as well punch the author in the face. Frankly if you don't see what is going to happen it's because you're asleep and skipped better chucks of it. The least it could have done was have Tatsuya unveiled as a badass in a fight, but no. By the first fight there were already several instances of Miyuki saying Tatsuya is more capable than her, but more than that, you have already seen Tatsuya in ninja training, so you already know Tatsuya is a ninja. All of the fights, being the explanation filled clusterfucks that they are, are just boring with outcomes made up way before the fight even starts. The story just lives by the motto "tell, don't show."

I wish I could like this, but it's just boring. No matter what I look at, I just can't find enough that I don't see huge faults in. The characters are all perfect(ly flat), almost all the conflict comes from unaffiliated parties that don't really care about Tatsuya and co. (they just happen to be working too close to him), there are no reveals as everything has already been explained, and simply put, the author never put time into actually writing a story that is interest.