Chiaki , Ryuuki’s childhood friend, is introduced more prominently. Her latent feelings for Ryuuki create a classic love triangle, as she suspects Ryuuki is hiding a significant secret.

Coming-of-age (seishun), summer nostalgia, emotional drama, subtle romance.

It seems you're looking for information about a specific anime or manga title, likely "Shounen ga Otona ni Natta Natsu" (少年が大人になった夏), which translates to "The Summer a Boy Became an Adult," and specifically its first three chapters (cap 1, 2, 3) with subtitles ("sub").

Shounen ga Otona ni Natta Natsu (translated as "The Summer the Boy Became an Adult"

– As Ryuuki spends more time with Kirill, he begins to "become a man," unaware that he is actually interacting with his sister. The tension between his feelings for his sister Reiko and the actress Kirill becomes a central theme. Adaptations and Availability