That first picture of Kiriyama hit me. I saw it and just thought, "Whoa, that's him? He looks like an adult!"
People keep talking about character growth, but it's the most striking when it's done through the art.
Like Shimada a few volumes ago. Before he used to be made fun of because he was about to become bald, then he started getting drawn with lushy hair and looked more handsome than ever to woo Akari (or at least to be a future prospect for her).
Usually, you can't draw mature characters right off the bat, or you will have a lot of trouble bettering the art later on. And doing so also makes the characters' aging feel way more natural, and it accentuates the passage of time in the plot, during important events needing it.