So I'm halfway through the series and if I look back, to the first volume I cannot say, that the characters developed whatsoever.
However that may not be considered bad in this case.
The reason for that is, that the characters are basically the core of the series. If you thought that the story was the strong point of this series, by my opinion, you are wrong. The series could be easily represented as an American sitcom (Seinfeld) where basically nothing happened and the story is about everyday life of the characters.
Thankfully there still is some development in Yoshii's romantic life, albeit slow, but hopefully we'll get there.
This volume was not as entertaining as the rest, neither was that funny. I do hope for an improvement, at least in the story development.