Airplane

Hikōki (ひこうき) is the 3rd chapter of the 2nd volume and the 8th chapter overall of the Attack on Titan: Lost Girls manga, written and illustrated by Ryōsuke Fuji.

Overview
While Eren recovers at home, Dr. Yeager takes Mikasa back to her home. On the boat, he tells her that his friend in the Garrison will look into the incident. He expresses worry for his son and believes Mikasa may be able to change Eren's mind. During later visits to the Ackerman family home, Eren is absent due to his injuries. Mikasa writes a letter to Eren and gives it to his father so he can receive it.

When winter comes, Dr. Yeager reveals that Mikasa's mother has pregnancy toxemia and must move to Shiganshina so that immediate care can be given. Mikasa wants to see Eren again, but his mother says he is busy with Armin. Dr. Yeager receives information from his friend Hannes about Eren's attackers. He sits with Mikasa and reveals that the two men who attacked Eren were killed in a carriage accident. He says the men got what they deserved, and later Mikasa sees images of her parents being attacked in her mind.

Eren reunites with Mikasa, having recovered from his injuries. He tells her that the Survey Corps has been disbanded and the gates to the Walls have been sealed, and that he and Armin plan to fly over the Walls in an airplane left by Armin's parents. Mikasa worries for Eren's safety, but promises to keep his plan a secret. Before he leaves to fly with Armin, Eren gives Mikasa his scarf and a caged butterfly, and Mikasa asks him not to die.

Summary
The morning after his beating, Eren watches a flock of flying birds outside his bedroom window while Mikasa sleeps in a chair beside his bed. Later during the day, Grisha Yeager prepares to take Mikasa back to her home and Carla apologizes to Mikasa for her not being able to have any fun after coming all the way into town. Before leaving Mikasa asks if she should go get Eren to which his parents reply telling her to let him sleep. On the boat, Grisha explains to Mikasa that he has a friend in the Garrison who he has asked to look into Eren's case. Grisha asks Mikasa for a clue as to start the investigation, however, Mikasa is reluctant to do so due to her promise to Eren. Grisha continues to explain that he worries that his son's rage will lead him to dangerous places. He decides that moving Eren to the mountains where Mikasa lives may be good for him. Grisha fears that there is a great but dangerous power inside Eren that only Mikasa can protect him from. They later arrive at Mikasa's home where her parents are waiting for her.

During Grisha's later visits to the Ackerman family household, Eren is absent due to his injuries. Mikasa asks her father for paper and a pen in order to write a letter to Eren. In her letter, she expresses her sadness due to not being able to see Eren. She gives the letter to Grisha during his next visit to pass it on to Eren.

When winter comes, Mikasa starts to fear that Eren will never come back and see her. During a visit to the Ackerman home, Grisha reveals that Mikasa's mother has pregnancy toxemia which might harm the baby should her condition get worse. He suggests that the Ackerman family should move to a home near his own in Shiganshina District so he can come right away in case something happens. Five days later, Grisha helps the Ackermans move to Shiganshina. Upon arriving Mikasa's father suggests that she should head to Eren's home to play. When Mikasa gets to Eren's house his mother says that he is off playing with a boy named Armin. Grisha received information about the men that attacked Eren. He sits with Mikasa and shows her drawings of the two men who attacked Eren. He asks Mikasa if these were the men who roughed Eren up and she nods in response. He reveals that the two men were killed in a carriage accident while running away from members of the Garrison. He says the men got what they deserved and later Mikasa sees images of her parents being attacked in her mind.

Eren finds her sitting in a chair spaced out and takes her out on a walk. While on the walk Mikasa asks Eren why he stopped visiting her. He shares with her that the Survey Corps has been shut down due to their lack of results and the gates have been sealed up. He tells her that he could not visit her anymore because he was busy building an airplane with Armin to fly over the walls. Eren explains that Armin's parents had tried to fly over the walls two years ago but failed and died, leaving behind a prototype in a secret location. He says that Armin is fixing what caused the original plane to fail. Mikasa thinks back to her conversation with Grisha on the boat returning to her home. She worries that even if she stops Eren from building the airplane he will just find another way to go outside the walls. She decides that the only way to protect Eren is to let him continue with his plan in hope that he will eventually give up on the outside world. She promises not to tell anyone about his plans.

On a later date, Eren gives Mikasa a caged butterfly explaining to her that Armin had built the cage. He tells her that the airplane is finished and that he will leave during the night. Mikasa asks him not to die and in response, he tells her that they will come back for her once they get settled outside the walls. Before walking away Eren wraps his scarf around Mikasa telling her to take good care of it while he is gone.