What a great manga, at least until the end.
The start is weak, where in a typical fashion the pampered princess falls for the first guy she sees. This is annoying to keep seeing, but fortunately she dies and becomes a zombie quickly so the main story can begin.
This manga had a great mix of drama, intrigue and romance. The drama, notably family melodrama, gave the story emotional punch. This keeps the reader engaged in the stories of each character as they live their lives. Intrigue was great here. The 60's style spy movie feeling given off by the zombie research was a treat. The romance was surprising. This should be listed as harem as multiple characters fall in love with Chihiro. Midway the romance becomes better with intrigue. The mangaka, through the story, built up to what would have been a masterpiece of an ending, with a twist on the tragedy tag.
He proceeds to torch his own creation with the ending, this being completely out of place for the quality the rest of the story showed. The complete lack of gut the mangaka had when writing this ending is frankly an insult to the reader.
A great story with an OK ending. 8/10 with the ending, 9/10 without it.