Chilling Hostility - S4.E6

Darius traps Illya inside an ice barrier Noble Phantasm which slowly cuts off her oxygen supply. Tanaka manages to break through the barrier, allowing the others to come to Illya's aid, but they are all helpless to fight against Darius. After taking an interest in Tanaka's abilities, Darius takes his leave, with Erica leaving some disturbing words for Illya. As Illya and the others try to figure out their next move, Darius performs a painful ritual with Miyu. The next day, Kuro discovers that Illya has disappeared, leaving her Class Cards behind.