Celeste Fairy

The Celeste Fairy (チェレステの妖精) is a short story written by Kawahara Reki and given with Dengeki Bunko magazine volume 31.

Summary
On Friday, 10th April, 2025, after Kirigaya Kazuto hangs his new school uniform, he hears a loud shout from his sister, Suguha, calling him to come down to the garden. When he gets down, Kazuto notices a large object, covered in a bed sheet, next to his sister. Suguha then tears off the sheet, revealing a Bianchi road bicycle. After Kazuto's onslaught of questions, Suguha reveals that she bought the bike with a huge discount from Rinrindou, a bicycle shop that the two frequented since kindergarten. While examining the bike, Kazuto notices that the bike is too big for his sister, whom then replies that the bike is a gift for him to celebrate his enrollment.

Two days later, 10 in the morning of Sunday, 12th April, Kazuto prepares for a cycling course. Just as he is about to exit into the main road with his bike, he calls out Yui, who appears in his AR sunglasses, connected to the mounted portable terminal on the bike. Kazuto asks Yui to begin data logging and barely dodges her question after accidentally letting out a remark about her Artificial Intelligence abilities.

After cycling for around twenty minutes, Yui suddenly detects electromagnetic waves of the ANT+ protocol coming from Kazuto's bike. At his request, Yui searches for the device transmitting the waves and visualizes a girl the size of Yui. The mysterious girl announces that 907 days have passed since the last ride and that she is being charged by the bike's internal dynamo. Kazuto then realizes that the reason why his bike was so cheap was because the previous owner built a power generator in the bottom bracket of the bike, which caused the bracket to get stuck and the bike to be sold for a much cheaper price. He also realizes that the battery was probably charged to the minimum level after the time he spent cycling, which caused the device storing the mysterious girl to start up.

Stopping in a parking lot to gather his thoughts together, Kazuto realizes that the previous owner of the bike wouldn't have left such a customized interface behind willingly, therefore he decides to find the previous owner and return the supposedly stolen bike to him. Having Yui to pass on his voice messages to the girl and finds out that she is named «Cel» and asks her to display the previous travelling route, revealing the previous owner's home.

Arriving at the destination, a detached house, Kazuto interacts with the intercom and explains the reason for his visit. A woman in her mid-twenties comes out and opens the gate, being taken aback the moment she saw the bike. The woman then explains that the bicycle used to belong to her younger brother, a university student, and explains that her brother was denied from riding bicycles due to a certain event in autumn three years ago that left him stuck in the bed for two years. She also explains that due to his weakened body, her brother has shut in his room playing VR games, refusing to go to university or to go cycling, because of this, the boy's father angrily got rid of the bike, which was supposed to have been a present to him for getting into university. Kazuto then asks the woman whether her brother would like to have his old data logger, the one storing Cel, back.

A little while after the woman sends a message to her brother via her terminal, a ringtone starts playing from the terminal. The caller explains how to safely remove the data logger from the bike and Kazuto gives it to the woman to pass it to her brother. After Kazuto shares his contact details with the woman, in case her brother ever decides to buy a new bicycle and come over to Kawagoe to thank him, Kazuto sets back on the cycling road to head back home. While cycling back, Yui reveals that she had communicated with Cel and got information on the road surface from her. Yui then asks whether they will ever get to see Cel again, to which Kazuto answers that he is sure that they will meet her again.