I will use some slight spoilers in this review, but nothing that should ruin your enjoyment of the manga. Also, I have to confess I have not read the sequel. I don't intend to do so for the near future.
To give credit where it is due, I think the author did have a solid story planned out from the start which was suppressed and lost due to the format. Had this been a LN, I think the author would have had a much better chance to develop his characters right and lay out the dynamics of the world. The pacing of the manga in the start is very slow -- and slower to lay out the exposition -- and it is extremely fast towards the end.
The plot of this manga is very confusing; to the point I would say that 'confusing' is an understatement. It starts out a bit like High School DxD, progresses quickly into a pace like Mx0 with less comedy, then we get a scenario a bit like Owari no Seraph and lapse off into an ending that invited the reader to continue reading in the next series. The lack of a conclusive ending did not contribute to my enjoyment of the series. Characters are introduced rather haphazardly and the world building is mediocre at best. Even by the end I didn't understand anything about Orvis or the way it is governed. I'm also not sure if it is just an academy or an entire city. The powers of the characters are also not scaled well. Readers are not explained the source of the character's magical powers or the reason for the variation in powers. This need not be a problem, but at many points in the story, characters have sudden power-ups that make little sense and the inability of the reader to gauge the sense of threat to the MCs makes each encounter less interesting. As a reader, I never found myself invested in the story, like I do for One Piece.
The art is actually fairly good and the fanservice is also not overtly scattered at odd-points in the panels. There were a few scenes where I thought the fanservice was badly placed, but it isn't too problematic.
The characters are where this manga scored really low. Characters are not consistent. The female MC was badass in the beginning and -- remarkably suddenly -- transforms into a lovestruck girl with low self-esteem. How she fell in love with our MC, I will never know. The male MC started out as a serious character, then seemed to become some average MC of a harem anime and then reverted to serious. The MCs friends are introduced and then forgotten rather quickly. The motivations of characters are never fully explained. We don't know anything about the teachers of this academy, or the motivation of the four leaders of this society, or even the real motivations of our MCs. Serin's motivations are especially confusing.
The overall muddle of the plot, the inconsistencies of the characters and the poorly-developed world makes for a less-than-enjoyable experience.
TL;DR: I would recommend people to skip this manga. If I eventually bring myself to read the sequel and form a better opinion of this, I'll revise my review here. It's just a messy series at all points.
