An illustration from the first volume can be seen here:
http://www.mediafactory.co.jp/bunkoj/books.php?id=22085
An illustration from the second volume can be seen here:
http://www.mediafactory.co.jp/bunkoj/books.php?id=22823
An illustration from the third volume can be seen here:
http://www.mediafactory.co.jp/bunkoj/books.php?id=23668
An illustration from the fourth volume can be seen here:
http://www.mediafactory.co.jp/bunkoj/books.php?id=24496