Aleister's Sacrifice And Power
Hearing Aleister's suggestion, not only Arceau but even Amelia was astonished by it. They didn't expect that Aleister would risk his life just to protect Arcadia in Arceau's stead.
Others might not know, but Arceau and Amelia knew what Aleister meant. Although there were still chances of Arceau surviving, the chances of him dying were higher if he used his secret move to deal with Keith's fist construct.
After all, Aleister wasn't a god yet while Keith's fist construct was still at the level of a god's attack even when its power was reduced by Arceau. Because of that, they knew that the chances of Aleister sacrificing his life when he used his trump card were higher.
But since Amelia didn't have the right to persuade Aleister since she was only a bystander in her current situation, she could only hope that Arceau managed to persuade Aleister.
And as Amelia had expected, Arceau started her persuasion in order to prevent Aleister from sacrificing his life.