Skip to the bottom for a tldr.
Art: not the most gorgeous illustrations I've seen, but really well matched to the dark themes involved in the story. 0 unnecessary ecchi despite the cover. Really helped set the atmosphere in my opinion. Very well matched to the story which is why I rated it 9/10; those who are looking to read a manga purely for the gorgeous illustrations however should look elsewhere.
Character: It actually did a pretty decent job of developing all the characters. The characters were pretty cookie-cutter but what can you expect with over 20 recurring characters that each had unique identities and stories? My
main gripe is that the main characters lacked in-depth development but it didn't detract from the story.
Story: Oh boy. Started out super interesting. Started out innocent enough and progressively got darker and darker and was paced very well in my opinion. But... Ending was so bad that it deserves a negative score, thus bringing down the average of the beginning and the end to 1. Yea, the ending was a plot twist but...wow...what a lame plot twist. Ghosts. The story was resolved by ghosts. Just...what? A story with lots of potential was brought to utter ruination by the ridiculous ending. I was willing to put up with the ridiculous premise of the enslaving mechanism because of how compelling the beginning and middle of the plot was, but the ending...imagine you are making the most mind blowingly enjoyable love with the love of your life who is willingly indulging in your wildest fantasies and loving it. You start out with the most tender, tantalizing foreplay, move on to the most passionate main course, and then, about 70% of the way through, a religious fundamentalist group barges in and castrates both of you without anesthesia. That's what this ending was. I really cannot understand why the author just threw in a ghost and ended the story when there were a million ways to end it off nicely but I can only review what I'm given.
Overall: Very much a story driven manga. The characters and the art are accessories to the story and they do an excellent job of being accessories. Problem is the story was just utter garbage. It had great potential but it was ruined by one of the worst endings I've ever seen.