I think that you could make a case for catharsis amongst several characters. In my mind, Sethe undergoes the greatest amount of catharsis. Her narrative in the work is one entirely predicated upon evolution and change. If we take the "purging of emotions" idea, then the appearance of Beloved, as a spirit, is what triggers Sethe to "come clean" about her own experiences and purge the past into the present. It is through this acknowledgement and acceptance that her perception moves from black and white and into color. Sethe is able to fully understand her role as a former slave, as a woman, and as a woman of color in a more clear light as a result of her being able to tell the story of what happened to her and her child. As Deborah Horvitz noted:
As the embodiment of Sethe's memories,the ghost Beloved enabled her to remember and tell the story of her past, and in so doing shows that between women words used to make and share a story have the power to heal.
Such a reality represents the essence of catharsis and character evolution throughout the course of the narrative.