Sister 3 - Catspaws is the twentieth story arc in the main canon of EGS. It opened Jul 4th 2016 (with a cover - which last happened with Sister II) and ended Aug 1st 2018.
Part 1: Legacy
The first part consists of Pandora's history - carefully written in a way so as not to reveal an exact date. Mostly it covers her relationship with Blaike Raven, which happened when she was 150 to 166 years old. Blaike was an adventurer, who attracted Pandora with his attitude - he didn't adventured for treasures, but just for the experience. He considered not knowing what's before him part of the adventure.
When Pandora was 156, she had a son - Adrian Raven - with Blaike.[1] She though that they will raise him together until Blaike dies of old age, which would be around the time she should reset anyway. But Blaike didn't died of old age, he was killed when Adrian was just 10, and Pandora didn't reset then nor later. She decided she will not forget her family and that she will be here for her son however long he lived.
Part 2: The Will of Magic
In the second part, Pandora enters Grace's dream and encounters the magical emissary. The two face off until they decide to communicate with each other. The magical emissary shares his mission and the fact that magic could change the way it works entirely. Pandora remembers an incident of this occurring from her previous self[2] and decides to fix the problem, surprising the emissary with confirmation it was her doing.
Pandora explains how the laws governing immortals are self-enforcing,[3] meaning that because she doesn't think she's breaking the laws, she isn't. After explaining the reasons she tried to change magic, the magical emissary informs her of griffin and Voltaire's actions the previous night.[4] Pandora vows revenge as she leaves to attempt to fix the energy problem, leading the magical emissary to conclude that his mission was never about talking to Grace.
Pandora approaches a sleepy Sarah and asks if she wants to "save all magic."
Part 3: Reply Hazy
In the third part, after a dramatic buildup, Edward Verres reveals to Nanase that Diane and Susan are not twins.[5] Knowing how Susan's father cheated, however, he notes that they may still be half-sisters. The two discuss the targeting of Diane and Susan by intelligent aberrations.