XIETIAN
My two guesses (more inclined to B)- A- Sirius threw the spear to help finish off the emperor, and it probably can't absorb the soul power, so all of it goes to Bai Zemin B- Sirius was waiting for Bai Zemin's fight to finish, so that he could throw the spear to earth and gift it to MC right as he returns. This would explain why some characters thought it wasn't really an "attack"- either to help Bai Zemin return to him or to get stronger, since destroying a planet will inevitably grab attention. As for the title- my guess is Bai Zemin and either Lilith or Sirius