in chapter 908 elders ask Imu which light needs to be erased from history
This chapter we find out that it's Lulusia kingdom.
Sabo being there was just
fate and him being
unlucky
Imu was not even going after Sabo
"erased from history"
since chapter 908 to 1060 whole of Wano arc and Reverie happened, meaning that it took Imu around ~1 month to prepare this attack with his spaceship
Imu is not strong. It even takes him 1 month to use an ancient weapon