Since it didn't happen in any other chapter and from what I can tell, it didn't seem to be like an artistic device, does anyone know why there were some raw/rough drawings in chapter 18 near the end when f181x

Niiya confesses to Yuuko?

Did the author run out of time before the issue deadline? 🤣

I know this question is a few months short of being a year old, but the reason for chapter 18 (magazine version, now fixed in the tankoubon version) turning out like that was due to the March 2011 Earthquake in Japan interrupting the mangaka's work.