Yuzu first meets him in chapter 2 where he introduces herself as his granddaughter, much to his anger. Later she does the same thing during assembly, causing his patience to run dangerously thin.
During her attempt to convince Mei to live with her again in chapter 3, Mei pushes her on a bed and begins to strip her. Yuzu just grabs Mei's hand and tells her everything is going to be okay. At this point, the chairman walks in to see a half naked Yuzu on the bed with Mei. Completely enraged, he expels her from the Academy.
Later on in the same chapter, she visits the chairman's house once more to convince Mei to come back home, and to convince the chairman to let her attend the school once more. She walks into his office to find him passed out on the floor, and quickly dials 911 (although we never get to see her dialing for an ambulance). The chairman, now grateful to Yuzu for calling the ambulance, revokes her expulsion.