Who is Sasaki in Jujutsu Kaisen? You need to rewatch one episode ASAP to understand

The seventh episode of Jujutsu Kaisen season 3 starts with a confusing shot. The camera slowly zooms in on a figure lying in bed, surrounded by a pitch-black void. A young woman with dark, messy hair opens her eyes and speaks to Kenjaku, who explains that she’s inside the barrier for one of the colonies that’s part of the Culling Game. She politely asks him not to do this in her neighborhood, and he even laughs. In the space between dream and reality, Kenjaku offers her the chance to wake up outside the barrier, and they walk hand-in-hand to get there.