Guide from FANDOM How to create a Hollow Princess:

Step 1: A Target must be installed into a Extraction Pool that is set to EXTRACT mode. Step 2: Wait Until the Soul Crystal Extraction is complete.

A completed Hollow Princess:

How to create a VOID QUEEN: (using Joyce as Incubator for Lisa) Step 1: At least two Target must be chosen in order to create a Void Queen. One will act as a incubator for the other, as a result, two Void Queen can be created at the same time.

Step 2: Install a foreign SOUL crystal into the Hollow Princess. (foreign: The SOUL crystal must not be the original owner of the Hollow Princess e.g. Lisa is installed with Joyce’s SOUL crystal)

Step 3: The Hollow Princess will take a “incubated” form, which looks like pregnancy. The corruption process will take a few days.

You can check the progress in the Pool machinery.

Step 4: Once the SOUL crystal have been corrupted into VOID crystal, extract the crystal from the Hollow Princess.

Step 5: Install the VOID crystal back into the original owner.

A completed Void Queen