Well yeah, it's usually a good idea to avoid the people who can rip you out of the body you stole and devour you, but I was referring specifically between Yazuko and Melody, since Melody fights unaffected by emotion and Yazuko's powers involve reading and manipulating those emotions. On the other hand, Yazuko is in the best position to fuck with Melody by intentionally activating her emotionless state from a distance (By forcing her to feel as much fear as she would when under attack)