It was said that this was the first and last of it's kind meaning that no such thing happened before this after Imu became ruler of the world!
I think Imu was shocked because not only someone managed to pull that off, but it was someone with the will to take him down and become the new king of the world, maybe Imu thought that this particular " will " vanished during the void century but here it was baring his fangs before him!
That's why the government went through such lengths to make sure Rocks D. Xebec's name and tales would be erased from historu so his will would not get passed down ( cuz how the fk do you hide this dude from history, they must've gone all out on making sure he's forgotten )
But here we are Black Beard, Loki ( he said that he would've been King of the world if he had made it all the way to the holy knights ) seem to have that will in them, that's also why Imu was really angry at Black Beard wanted poster cuz not only he looks like Rocks lol but he is also doing all the things Rocks did like taking Hachinosu etc etc
Do you guys think it's plausible ?