This is another thing that has been posted, but not as often, given how useful it can be.You can avoid having one of your characters being cursed by Al-Sedexus if you kill her the first time you meet her (go into combat mode instead of talking to her). She'll still show up for the Templar quest, but your character will not be cursed afterward.
This was useful in my last game... I went through the Rapax area and got all of the good equipment, and then went through Bayjin, and it was a breeze.
I'd be careful about killing any of the Templars she summons, though... if you kill too many, it might lower your rating with them, and then you won't be able to even do the Templar quest. After killing her, just run like mad from the battle and enter the teleporter shortly outside of where you encounter the demoness. The Templars she summons will not follow you. Though, can anyone verify if killing them (when you first meet Al) will indeed prevent you from completing the Templar quest?
If you do wait to fight her later, it's still wise to avoid fighting the Templars, since it will lower your rating (well, you can get a way with killing a couple). Killing her won't lower your rating, though, which is a good thing