|… Firefly's Promise.|
|Season 1, Episode 05|
|Air date||November 10, 2009|
While trying to learn about reading a picture book to the children, Kobato meets the author of the book, who asks her to not read it anymore. Wondering about his strange request, she decides to find a way to cheer him up, and in the process gains another konpeito.
The kids in the nursery asked Kobato to read a picture book but she fails to read it to them properly. She continues to practice reading at a park as a result until a man approached her and urges her to stop reading the book she's at. Kobato, saying nonsense in an attempt to know why, leaves the man withdrawing without explaining. And at the nursery earlier, Sayaka receives a phone call that makes her anxious. Kobato wakes up late for work, and are greeted by three men who look like people working for a loan shark. They demand payment from Sayaka, who is present, and the men soon get tediously rough. Fujimoto was there, but it was Kobato who defends Sayaka despite her fear. Toshihiko cries out loud for the police to come, taunting the men to leave the nursery, which they did. Later on after work, Kobato wants to figure out a way to help Sayaka with her loans but her troubles shifted to the man he met the previous day in the park. She goes to him tried to convince him to get her to help him but he only requested her to not to read the book again. Kobato returned to the apartment only to find out that Fujimoto too is staying there too. She told him about the man she met earlier whom Fujimoto referred to as Mr. Mori. It turns out Mori Soutaro is the author of the picture book and the book is apparently the last one he ever written.
Kobato began to read out the book, Hotaru no Hikari. It goes about a single firefly who is living alone by a river stream. Having staying alone for the longest time, he forgot the fact he was a firefly at all. One night, he was approached by a female firefly who is able to glow her light. He asked her who she is and she replied that she is a firefly same as him. She then asked him why he did not glow like her. He said that he had been staying alone for so long that he forgotten how. She helped to teach him to glow again and in the end, he did. They both finally lived together happily at the riverside. Ioryogi likened the firefly to Mori as he said that Mori forgotten how to glow himself (please don’t misread glow with blow). Kobato got an idea of how to help him by bringing him to a spot where fireflies are. He did come but to no avail, not a single firefly spotted. He however was willing to tell Kobato his love story with his girlfriend, Naoko. She was also the one who drew the picture for the book and gave him the idea to write the book in the first place. It was her who invited him to go to see fireflies at the same spot last time. He was busy with work then and could not find time to join her. One day, he did but she did not show up. She got into an accident and did not survive. Her final words are to see the fireflies together. Since then, Mori blamed himself not being able to be there for her and with that, he decided to leave the place. Kobato tried to convince him to stop when they reached a place where Naoko was to draw a picture for the book. Almost instantaneously, fireflies began to glow around the area and astonished them both. At this point, I believed Mori came to terms with his sorrow of a promise he made with Naoko.
Days later, he resumed his writing career and Kobato received another konpeitto for her efforts.
- The Book Hotaru no Hikari Shares the Same Name as the Song Hotaru no Hikari By Ikimono-Gakari.