@verus: I'm guessing that Katase is strictly speaking only responsible for Shiozaki, whereas Hayakawa is simply a junior coworker in the same department that frequently interacts with both of those two in both professional and non-professional capacities. Think of it as Hayakawa technically being part of a separate chain of command from Katase and Shiozaki. Makes you wonder who's her "senpai", if she even has one.