Summer Pockets Short Stories ~In the brightness of summer~
「Summer Pockets」ショートストーリー ～夏の眩しさの中で～

Written by the original authors, the series contains prequels that were not told in the main story of Summer Pockets and secret stories that happened behind the scenes.
サマポケの本編では語られなかった前日譚や、物語の裏側で起こっていた秘話をオリジナルライターたちが執筆

The illustrator is Humuyun.

Source: https://key.visualarts.gr.jp/summer/special_ss.html