"The Gentlemen alliance".
Well, is a Tanemura´s one. (I think is the newest, after Fullmoon wo Sagashite)
I really like it. The drawings are really really great, and the story is very interesting now (the begginig was a little... weird?... slow?)
I think is the longest one too, 'cuase it has more than 7 volumes.

Does anyone know this manga?

Here some images