Yue and Kouki are at times the child and at other times the parent for one another. Isn't life like that sometimes?! ^_^ No one can play one role all the time; this manga handles this issue very well.
The characters are multi-dimensional; the dialogue and inner thoughts are deep and grounded in solid psychology. The only thing that was slightly unbelievable was that Yue was TWO times lucky that her bf's were so understanding...or maybe unlucky since they didn't fight for her...
The relationship between the daughter and father is complicated with a very real feeling. The mother, who is already dead at story's beginning, plays an important role, not just a cheap reason to make the relationship 'forbidden'. At the same time, the 'forbidden love' theme is really intense and exciting, even with the quiet sorts of stories that the mangaka weaves that reveal a lot about the depth of their relationship.
She matures slowly as she meets and deals with other people; all in all it was really well delivered as a 'growing up' story without being boring. Simple topics like finding value in cooking and cleaning for the one you love are delivered with great, humanistic impact. Openly complicated issues, such as dealing with death and grief and how each person helps and gives to the other unknowingly are also delivered beautifully.
The pacing was surprisingly fast for this mostly emotion-based story. The art is bishoujo and pretty, smooth and flowing like water. I like my men in shoujo/seinen to be a bit more manly looking than this overly-pretty style, but it was easily overlooked because of the narration excellence.
Until you get to the '2 years later' part...
It is a realistic and interesting solution/answer to their problems, but it was delivered so very fast with so many things unanswered and didn't match the careful delivery of the rest of the story. And there was never an absolution or consummation, which was very disappointing, since the whole story did build to a physical moment that never comes.
Koukando Equals was short, tightly written with a nice little moral, without being dogmatic. Diamonds I didn't read.
PS: Shoujo Magic's inserts often feature a single piece of artwork framed within a coloured background and accompanied by a touching quote. I look forward to these delights!