"GJ Bu ◎" by Araki Shin. This was published between "GJ Bu Chuutoubu" volumes 4 and 5, and contains some extra episodes to fill in missing details from the original "GJ Bu" novel series.
A feature of this volume is that there are 3 longer chapters, breaking away from the usual 4-koma format. Even without the extra illustrations or the consistent tempo, the characters are still fun to follow. If people ever wondered what this series would look like if it was written in the usual novel format instead of its unique 4-koma style: it goes quite well.
Previous (2013-06-20): "GJ Bu Chuutoubu" volume 1 by Araki Shin
Next (2013-07-18): "A Skeptic's Guide to the Mind" by Robert Burton