A whole chapter devoted to the leader of Urumin's group. This is the kind of backstory that the author can spend time to tell now that the story is serialized. I have recently been watching Zombie Land Saga and Airu here reminds me of Saki from that show. They are both former delinquents and the leaders of their respective groups.
It was also nice to see our brave MC Kimiya on the last page. He must have been a fan from the very early days.
It's really impressive how the mangaka's expanding on things in the serialized version.
IIRC, we did get to see Airu the first time through, but only briefly and in idol mode - we didn't get even a hint of her background until just now. And the way it played out - slipping into her old delinquent mode just long enough to deal with those guys, then switching to idol mode to win then over as fans - was brilliant.
And the other girl covering Urumin's eyes was a great touch, and funny to boot.