Quick Review
Writing Quality: Very few grammatical errors, if I had to say a recommendation, I'd say to have fewer words in each paragraph, it makes it easier to read.
Stability of Updates: Unknown since I just caught up.
Story Development: So-so, at least for the moment, it follows the cannon of DxD completely with some minor changes here and there.
Character Development: So-so as well, If I had to highlight something is how Sephiroth seems to grow as a person little by little, this is a good approach, the issue is they way you portray that change, I'll explain myself further shortly.
World Background: So-so, there's minimal Ambiental description in each scene and so far there's just Kuoh Academy, Kyoto and some places in the underworld, the former complaint is the reason why I give a lower score.
Now to get into details I think it would be easier to highlight what is good and what is bad.
What is well done:
1.- I don't know Sephiroth very well, but his indifferent attitude is obvious, he's also rather honourable and even though you somehow push the R18 into him (I kind of don't imagine him acting the way he did during both instances) you could say it is acceptable (I'd actually put some femdom with Yasaka, as you could say she's more experimented while he's a newbie in the matter, yet they were portrayed as to have the same experience, he even managed to dominate her...).
2.- I like that he doesn't involve himself with women easily just because Yolo, he's kind of loyal at least comparing him with most fanfics.
3.- Bro that battle in the underworld, I was about to drop until I read that, nicely done there man.
4.- I like that he's focused, his goal is to get stronger, and getting stronger he does, the harem and everything are on the side.
5.- I like that you don't discriminate characters or have bias except for one instance and that is RIAS.
What I believe is not well done:
1.- You didn't do proper research about the characters and their levels of power for instance: Tiamat should be way above Yasaka in power, her power should be above the other satans except for Sirzechs the only reasons she lays down in the story is because of her own convenience, not because she's weak.
2.- Although this one I think you fixed, I'll mention it anyway and that is: The battles need a better description and improvement in the sequence. I say that you improved because the battle against Tiamat was so boring and horrible that I wanted to cry. I mean fking Dragon King and the best she could do was spit some flames? yet you totally remedied yourself with the battle in the underworld, that was so much better and entertaining 'This is totally Sephiroth' those were my thoughts.
3.- There are several plotholes, for example: In their second meeting, Sona, Rias and Akeno should've known Kunou already.
4.- The OC you made Chaos is totally lacking from the story, I don't know if you've got plans for her but her involvement in the story, totally contradicts what she represents, I would understand if Sephiroth was her employee or if she just reincarnated him and just disappeared but since He belongs to her be it, husband, lover, slave or whatever (As far as I can see they should have a Master-slave relationship) but she proclaims herself as his wife so it is difficult to me to comprehend that such goddess is alright with sharing when measly mortals like Kunou, Rias and Akeno, aren't.
Much more so when it was Yasaka who got his virginity first and not her (if it was some other character or some other circumstances I'd give a shit but this is Sephiroth we're talking about a completely asexual character)
Basically, you could take Chaos out of this novel and nothing would change.
Overall, this novel is entertaining.
