Diabolos had a simple reason for searching for Aion. Though Aion was a demon, he had rebelled against the Demon World and taken away the Demon World's head—because of this, the fixed boundary between light and darkness had begun to blur. If they did not find Aion soon and reclaim the Demon World's head, the boundary between Heaven and Hell would collapse. When that happened, not only would the Human World suffer, but the Demon World would be dragged down as well.
That was why Diabolos, despite being a demon duke, was willing to work with his mortal enemy. From Makdara Monastery's standpoint, after all, they certainly did not want to see the world collapse either.
Unfortunately, even Chrono, who had once been Aion's companion, did not know what Aion intended to do. But no matter what, the bastard had first taken the Demon World's most precious treasure, then set his sights on the Earthly Agent. Clearly, he was up to no good.
In the end, the three parties reached an agreement.
Diabolos would provide intelligence, Makdara Monastery, where Rosette belonged, would act on that intelligence, and Shizuku would remain at the center—put bluntly, her task was to protect Eris. According to the information they had, Aion needed to find the Earthly Agent to carry out his plan. As long as Eris remained here, no matter how perfect his plan was, he could not put it into action.
And if Aion dared appear before Shizuku, she guaranteed he would not survive three seconds—the anime's ending had been far too frustrating. If she did not take this bastard, first divide him into ten pounds of lean meat and mince it finely; then divide another ten pounds of fatty meat, with no lean mixed in, and mince that finely too; and finally