Walls is the 28th chapter Ajin: Demi-Human, created by Gamon Sakurai.
After Takeshi Kotobuki escaped, he refused to explain how to the prison guards and was held in solitary confinement. Eventually they prison warden decided to forget the entire incident and sent to his new room where he met Kai.
Later on, one of the prisoners threatened Kotobuki trying to learn how he escaped but Kotobuki refused to give him any information. Soon Kai interrupted them and got beaten up for it. Kotobuki tells Kai to stay out of his business and reminds Kai that he got left behind by his friend after he tried to protect him.
After going to sleep, some of the prisoners attacked Kotobuki again and breaks his arm. He looks over at Kai thinking that he's better off pretending to sleep. While being attacked Kotobuki thinks back to when he escaped after seeing Satō's announcement dismissing it as a stupid whim. Kai soon intervenes but was outmatched. Kotobuki watches this thinking that Kai was a total idiot. He soon helps Kai and knocks the other prisoners out. As Kai loses consciousness he sees an IBM.
The next day, Kotobuki offers Kai some cigarettes and asks Kai about Kei Nagai. Kai tells him that Kei was his first friend and if he is ever in trouble he will go and save him. Kotobuki offers his to help Kai escape if he even needs to and reveals his winged IBM.