First, they had to determine exactly what ultimate move Charlotte Linlin had used in the battle at Marine Branch G1. Knocking down three of the world's top powerhouses in a single blow was simply terrifying.
Unless they got to the bottom of it, neither the Five Elders nor the Marine commanders would be able to sleep soundly.
At first, the Marines suspected that Charlotte Linlin had learned the Elbaf Giants' secret technique, Elbaf Spear. Both its power and the spectacle of its release seemed similar.
However, the officers and soldiers who had transported supplies from Branch G3 to Elbaf learned that the relationship between the two sides remained terrible. After Garp had figured out Charlotte Linlin's true strength, he also believed that even Elbaf Spear should not have allowed her to knock down three people from such a great distance in one blow. Asu's escape showed that he would not have been able to stop it even if he had stayed.
Furthermore, before unleashing the move, Charlotte Linlin had continuously used her abilities to create things that blocked and deceived her enemies' Observation Haki. Most likely, the move required an extremely long preparation time, and she feared being interrupted.
Based on those two points, Vice Admiral Tsuru, the widely knowledgeable Great Staff Officer of Marine Headquarters, had already vaguely guessed the truth.
However, the Pudding Kingdom was a World Government member nation, unlike the Faros Kingdom, which had withdrawn from the alliance long ago. Moreover, they were investigating rather than destroying a nation, so even a Buster Call was unsuitable. The Marines truly could not intervene conveniently.
Thus, "Steel Bone" Kong conveyed Vice Admiral Tsuru's conjecture to the Five Elders. The Five Elders then wisely handed the task to CP9, the organization that had always operated in secrecy and specialized