"But, there is still one problem left. And that is to find out who is the sender of the blackmail material. After all, it wasn't Seieki who obtained the blackmail material, but it was sent to him by an unknown sender."
Allen reminded Iris in case she forgot about it. He didn't forget about that since he was quite wary of the person who was able to obtain footage from the spy gadgets that came from the Supreme Academy.
This only means that the unknown sender of the blackmail material was likely someone who has connections with the Supreme Academy or was part of the Supreme Academy staff.
"Iris, when you hacked on every device of the
Allen asked Iris since he remembered that Iris had hacked through every device of Seieki's to delete all blackmail materials he had against Sophie and the rest of the class.