Tankoubon, or better known as Graphic Novels, compile manga chapters into book format. Below you can find release date information as well as ISBN numbers to help you track down a copy of your own. ISBN numbers are for Japanese editions only. There are 12 volumes total for the GK series.
Bunko, or pocket editions, are smaller versions of the tankoubon. They compress the series into a smaller amount of volumes to make it easier for new readers to collect. Bunko have no extras like the authors comments, or extra illustrations. Its just the manga nothing more, nothing less.
Official Fan Book
Official Fan Book - Hoshi no rasen
The book to your left, is known as volume 9.5 the official fan book (because it was released between issues 9 and 10 of the tankoubon!). This book has various illustrations in it, along with information regarding different aspects of the series. This book has not been translated into English by Viz Media, and is only available in its original Japanese release. It is soft cover, and the same size as a Tankoubon.
The Genbu Kaiden novel is a side stories centering around the back story of Rumido and Souren. Written by Madoka Takadono, and illustrated by Yuu Watase. There has only been one novel made for the Genbu gang thus far. Below the novel "Kizuna - Harukanru kaze no kora" was released in two editions: a regular edition, and then a special edition. While the contents are the same, the special edition sports a different cover, and comes with a 30 minute mini drama CD (omake).