Chains

Kusari (鎖) is the 1st chapter of the 16th volume and the 63rd chapter overall of the Attack on Titan manga, written and illustrated by Hajime Isayama.

Overview
With Eren still held captive below the Reiss family chapel, Rod Reiss explains the history of Historia's half-sister, Frieda, and her eventual fate after the family's encounter with Grisha Yeager during the fall of Wall Maria five years ago. Rod reveals that Grisha, in his Titan form, fought and defeated Frieda and stole her Titan powers, with the intent on ending the Reiss family bloodline forever. Meanwhile, with the success of the revolution fresh out of its core, an uncertain tension arises between Erwin Smith, Pixis and Darius Zackly. With Rod in the final stage of his plans, Erwin, the entire military and Levi's squad prepare to lay siege against the chapel to rescue Eren and stop Reiss once and for all.

Summary
Historia's memories of the dark-haired girl Frieda Reiss come flooding back when she and Rod touch Eren. Historia wonders how she forgot someone so important to her, since Frieda taught a young Historia to read, write, and was overall very kind to her. Rod confirms that not only is Frieda her half-sister, but that she also erased Historia's memories of her to possibly "protect her." Historia then asks Rod where Frieda is now to thank her for being there for her. Rod reveals that Frieda is no longer alive, and that Grisha Yeager killed Rod's family five years prior.

A flashback sequence shows Grisha Yeager, appearing rather distressed, meeting with the Reiss family in the cave below the chapel. Rod claims that Grisha came to steal Frieda's Titan powers. After killing and eating Frieda, Grisha then goes on to kill other Reiss family members. Rod's wife, 10-year-old Florian, 12-year-old Abel, 14-year-old Dirk, and the eldest son Ulklin, were all killed by Grisha. Rod is seen fleeing the scene above ground, with Grisha's Titan breaking out of the chapel. Back to the present, Historia wonders how Grisha could do such things, while looking at a wide-eyed Eren. Kenny appears and reminds Rod and company that the Corps' coup has succeeded and could be coming at any moment now. After complaining that he needs to use the restroom, Rod pardons him.

The scene switches to Zackly humiliating an upside-down noble, commanding him to digest "his food in reverse." This noble insinuates that "noble blood" like his is unaffected by Reiss mind wipes, while "slave blood" is susceptible. This proves to Pixis that said mind wipes are real and can undermine the revolutionary efforts taken thus far with the obtainment of Eren's "scream." Pixis also admits he knew of Zackley's torturous ambitions, and laments how humanity has turned against once another so soon after the successful coup. Erwin asserts that such interpersonal abuse will occur as long as there is more than one person alive. Erwin begins the Eren/Historia rescue mission and leads his forces to the chapel on the Reiss family grounds.

Another scene switch to Levi and company, also on the way to the chapel. Levi makes it clear that Kenny Ackerman is too formidable of a foe, thanks to the Anti-Personnel Vertical Maneuvering Equipment. Hange is hopeful that Levi and company have a chance against him since Kenny had started using said equipment the day prior. Hange also wonders why Levi knows so little about Kenny considering their apparent history together. Levi says he didn't even know Kenny was an Ackerman until yesterday, and then asks Mikasa if they are related at all. Mikasa says that her father's bloodline had apparently been persecuted in the cities, forcing him unto the mountains near the wall. Mr. Ackerman found companionship in Mikasa's mother, who was also persecuted due to her race. Levi asks Mikasa if she ever felt a moment where her body was imbued with power. Mikasa recalls the kidnapping event where she wielded a knife to save a young Eren. Levi says both Kenny and he experienced a similar moment.

Back in the cavern, Historia looks at Eren with a disdainful expression. Once left alone with Eren and Historia, Rod comes back with a black handbag. Rod retrieves a case with a syringe that Eren instantly recognizes from the night Grisha injected him. Rod tells Historia that Frieda is not exactly "dead" and still lives on as memories. Rod asks Historia if she wants to meet Frieda, paralleled to Grisha entrusting a young Eren with the task of avenging Carla Yeager prior to his injection. Aware that Historia is poised to experience the same event he did, Eren struggles to break free from his chains.