Numerous times near the beginning of the week, it's commented on how "an incredible urge to kill" was approaching the character, but then would stop and go away. It's implied that this is Rin/Lancer or Rani/Beserker setting up an attack but then not able to go through with it. While a Berserker would make sense; the exact same dialogue is for Lancer's path as well. What was happening was that the 6th Master was fighting the resurrected Julius; which is why his pin was in the fountain. It was a combination of this and dealing with conflicting emotions in fighting the main character that lead to the events of the 6th week.