Sassan is a character on Sentinel Island. She was Laiken's lover, and was killed during a ritual he performed that required "the blood of a loved one." An abomination was made of her body when it was later reanimated by necromancy (see Dead Sassan).
Sassan helps you break into the Battle Tower and take it over. To do this, you must complete The Second Coming, a quest she will give to you when first encountered as Sassan Ghost. With the help of the player her soul becomes her mortal body again.
Afterwards she is located in your bedroom at the Battle Tower. She helps you by giving you information about your tower and the people in it. She is also serves as a merchant, and is the person you need to speak after completing the tower's platform quests to have them upgraded. You can mindread her for 1400 exp to gain one skill point as well.
She initially has a low quantity of gold so she is not the best person to sell items to. She has a limited selection of jewelry (including the unique Elven Earrings and Darling Ring), and other items such as potions, charms, herbs, and formulas for sale.