Shinseki No Ko To O Tomori [upd]

While this theme appears in various casual stories, it is most notably associated with a specific series or theme in adult-oriented manga or visual media, often titled similarly (e.g., Shinseki no Ko to Otomari da kara ).

I assume you're referring to the Japanese phrase "" (Shinseiki no Kodama to Ōtome), which roughly translates to "The Tree of the New Century and the Maiden". However, without more context, I'll provide a general essay on the topic. shinseki no ko to o tomori