C
Kuzan spared Robin because he thinks of Robin's escape as Saul's dying wish, so he allowed her to run around until she meets a place she could call home. Kuzan never intended to kill the SH crew back when they met him. He was telling them they'd eventually face issues if they were with Robin meaning he didn't intend to kill them. He attacked them because he decided to teach them a lesson about what'll happen if they were around Robin. It's because Kuzan thinks Saul is dead that he couldn't bring himself to kill Robin—that's why he references Saul when he meets Robin after EL.