Sucking off mana is not exactly mandatory, it just helps to dramatically shorten the fight.
Basically, you need to continue Selena story until the outfit is available in the outfit shop. To make it a bit less spoilery, it includes the machine in Dirn Khibar, Elith and Cephrina.
Thanks for the info, I will see how I get on. I have also lost my charm spell and Celica has lost around half of her health points. That has happened since interacting with Cephrina and letting the Genie enter Celica, have I done something wrong?
