This suggests a private, unrepeatable archive of growth. It’s a "limited edition" version of a person that no longer exists because they’ve already changed.
Shounen ga Otona ni Natta Natsu (translated as "The Summer a Boy Became an Adult" ) refers to an adult-oriented hentai manga by the author , which was first released in Japan around October 2022 240906 shounen ga otona ni natta natsu vol1 exclusive