It was then compiled in a collection named Rohan Kishibe Does Not Frolic with three other stories, which released for sale on July 19, 2018. Yuyanagidai is on pages 61–116 in the volume.
Summary
Rohan sketches children playing in the park in search of the reality necessary for drawing his next one-shot work. Rohan is about to leave before being treated as a suspicious person, but notices that one child is touching his sketchbook. Rohan tells him to apologize for tampering with his work tools, but the boy doesn't. After a while, his mother appears and apologizes on behalf of her son. She tells Rohan a mysterious story about the reason why he "does not apologize".
The boy, Ken-chan (ケンちゃん), was playing at a park in Yuyanagidai where they used to live when he was suddenly attacked by a laughing black monkey. Since then, Ken could no longer speak. Curious, Rohan asks Ken to sketch the monkey.