I have mixed feelings about this.
The art is absolutely wonderful. It reminds me of other artists at some points, yet has it's own original and unique style. Some characters' appearances, however, can be quite confusing for those who don't pay attention.
The character personalities, however, are well done for those who are brought into depth. The villain believable, blinded by his goals to remember other things. The heroine is strong and confidant, and the leading male is comedic relief with a deeper, darker side. The other characters are just made out to look cool and don't seem to have much of a purpose in the story whatsoever.
Despite these slight problems, I enjoyed the story throughout the beginning and middle. It had twists and depth, but there is one thing that bothers me, and leads to the entire manga's downfall: The ending.
I won't spoil the ending, but I am one of many readers who are far beyond disappointed. It's ended abruptly and horribly, with no sense of reason besides the fact that the mangaka grew lazy and came up with a finale that dropped all of the series' potential. It leaves several important questions unanswered (such as why a certain event did not occur if it was clearly stated it should have happened) and the other outcomes unknown (one character is completely forgotten and never mentioned again as soon as the final battle begins, when they are the main reason the whole battle is occurring anyway!)
I'll tell potential readers this who dare to read this far: There is no happily ever after or romance if you're looking for that sort of thing. It's a tragic story with supernatural elements. The entire story was brought to a premature ending, and it's quite clear that lazyness had taken its toll on the creator. The last chapter finally tells the tale of friendship at its strongest, only for the final pages to tear it all way and wonder why it was ended in such a way.