This is one of the most important volumes in the main series, as it is a big turning point for Ilay and his understanding. It's actually peak delulu mode for him, because he is okay doing or saying one thing, but the moment he receives a similar reply from Taeui, he turns into serial killer vibe.
But that is partly why we like him! He actually exhibits some growth and in the extra chapter, we see how he works it out in his head. Is he full of himself? Yes, he is. He does not understand how average people communicate, but in the other sense that makes him pure... apart from psychotic that could not care less about other people apart Taeui.
There are also some reunions happening in this volume and we are getting closer to the climax of the story!