For those who never seen Japanese or Chinese ghost busting or vampire slaying, that's what Itsuki was doing, just much more high tech.
She first sets up a magical barrier with talisman or seals to trap the headless ghost, then uses Sonic, instead of prayers to subdue it. Then Ul acts as a medium to set up a communication channel between the ghost and the living. It just looks much more convenient and neat in the future lol
The giant chainsaw should be Xanthippe or some other minion of Nerval. Its sawing away a part of the colony and stealing it, probably gathering parts to help build a new body for Nerval.