It took me a long time to decide whether to rate this manga with a 9 or with a 10.
As the manga review states, Takashi -a very intelligent and kind boy- starts behaving strangely as his 17th birthday approaches. He becomes cold, isolated and even cruel. And something tragic happens because of that. His cousin -who is the same age as him- starts investigating, and strange things start happening to him as well.
I can say, without fear of writing a spoiler, that this is a ghost story... because it is already crystal clear by the second or third chapter, that there is a ghost involved.
The rest, however, I will leave for you to discover, as you read.
The story is really intriguing, and it keeps you hooked. The plot is very good, so are the characters. I also like the art, which is very realistic, and has very good backgrounds too.
The only reserve I have lies in the last two chapters. It isn't that I don't like the way the manga ends... the ending is fine, but I have certain issues with the way it was narrated.
The 13th chapter is too explanatory. I don't like it when I am explained things I have already realized myself... readers should be trusted more. But it isn't that much of an issue... as it's only a couple of pages I would get rid of.
The last chapter gets a little bit messy at a particular point... unlike the rest of the manga, which has a great pace and is very clear, despite the strange things that happen.
These two issues are what prevented me from rating "Sugiru Juunana no Haru" with a 10... but, the manga is definitely worth reading.