The Seventh Sister is voiced by Sarah Michelle Gellar, real life wife of Freddie Prinze Jr., who voices Kanan Jarrus.
Similar Clone Wars era medical space stations were seen in Star Wars: The Clone Wars (2008), Shadow of Malevolence (2008) and Destroy Malevolence (2008).
The title is derived from Yoda's line spoken at the end of Star Wars: Episode I - Die dunkle Bedrohung (1999): "Always two there are, no more... no less. A master and an apprentice".
First appearance of new Inquisitor The Seventh Sister and second appearance of The Fifth Brother.
According to Kilian Plunkett in "The Art of Star Wars Rebels" book, the shape of the Seventh Sister's helmet is based on that of the headgear worn by the Nightsisters in Star Wars: The Clone Wars (2008).