Lazuli.'s new song "unforgettable summer" was created with the theme of the summer of 2023. A song featuring Poston., who is active as a singer, on the vocal of feat. The jacket illustration will continue to be in charge of Tenrei, who will be in charge of the illustration after 2022. It is the theme song of "Remembering summer memories" with no options, and it is the first lyrics from a writer's point of view.